(MONEY Magazine) – From Swiss Army Knives to peanut butter and jelly in a single jar, there's a long and happy tradition of merging several products into one. So it's no surprise that electronics makers have taken to bombarding us with devices that combine two or three gizmos in a single unit. Many of us already rely on several electronic doodads, and the best of the new combos, or "hybrids," clearly improve on the components taken separately. Some increase the convenience of the stand-alone versions; others lighten your daily load; a few even save money. In these cases, the whole really is better than the sum of the parts.

With all too many of these products, however, the logic behind the merger is fuzzy at best. What gives? Well, with a certain amount of market saturation coinciding with a softening economy, manufacturers appear desperate to find the next big thing. Hybrids, which require no real technological innovation, are relatively inexpensive to get to market--so much so, says Gartner analyst Ken Dulaney, that many manufacturers are willing to test every possible permutation in the hope that one hits pay dirt. "Like a venture-capital firm," he says.

That may be good business strategy, but you don't have to play the guinea pig. We tested the hottest hybrids to distinguish the smart from the senseless. Here's what we found.

CELL PHONE + PDA

What were they thinking? Many of us already carry both. And to make calls, you often consult your PDA.

Greater than the sum of its parts? Absolutely. In fact, we think this idea may prove to be a genuine killer app. Kyocera's QCP 6035 Smartphone ($499), which makes its debut this spring, may not ultimately dominate the category (future versions will surely be smaller), but it's a vast improvement over previous cell phone/PDAs, which were awfully bulky. At seven ounces, it's just slightly bigger than a standard cell phone. Flipping the keypad open reveals a two-inch-square PDA screen. Best of all--and unlike most competitors--it uses Palm's operating system.

Even the price is an improvement over the separate products: You're getting the power and features of a Palm VIIx, including wireless e-mail and Web access, plus a full-featured cell phone for little more than the price of the Palm alone. A speakerphone and earphone jack make it easy to use the PDA while talking on the phone. And the phone automatically dials numbers you call up on the screen.

Slightly smaller than the Kyocera, LG InfoComm's TP-3000 ($399) doesn't use the Palm operating system and thus can't run the myriad programs for that platform. But if you'll stick with the calendar and contact-info functions anyway, it's a fine, less expensive alternative.

Expect even more competition soon. Cell-phone giant Ericsson is about to introduce its own non-Palm entry, and Motorola and Samsung each have a Palm-based version in the works.

GAME CONSOLE + DVD PLAYER

What were they thinking? Both connect to TVs. And the basic technology is the same. Why not make a unit that does both?

Greater than the sum of its parts? For the most part, yes. We've long felt that a shortcoming of any hybrid is that if it breaks down you have to replace two functions, not just one. To win our approval, any hybrid has to tackle that inherent flaw. Sony's PlayStation 2 does, if for no other reason than economics. Consider that a DVD player of comparable quality to the one inside a PS2 costs about $200. In effect, then, for just $99 more, you're getting what is widely considered the best gaming machine on the market. Indeed, we tested EA Sports' Madden NFL 2001 football game and found the graphics and sound to be truly amazing. There's one catch: Sony's much publicized supply problems.

CELL PHONE + RADIO

What were they thinking? When not chatting on your cell phone, you might as well listen to the radio.

Greater than the sum of its parts? Yes--but at first we didn't think so. There's no obvious synergy between a phone and a radio. Plus, radio just seemed a bit mundane in these high-tech times. But when we mentioned Motorola's V2282 to friends, it got a consistently enthusiastic response--especially when we emphasized two key factors. First, at only $99, it's barely (if at all) more expensive than a similar phone without a radio. Second, the radio doesn't detract at all from the phone itself: It's the same size as many cell phones. And the radio doesn't significantly tax the battery. In the end, it amounts to a fun bonus feature with minimal costs. One thing to note: The V2282 cell-phone service works only on GSM networks, primarily in large cities.

DIGITAL CAMERA + WIRELESS NET ACCESS

What were they thinking? Many digital photos make their way to the Web via a computer. Why not go direct?

Greater than the sum of its parts? Yes, but at too great a cost. While the idea of snapping a picture and instantly sending it via e-mail or putting it on the Web has appeal, few of us have a compelling need to do so. And at $1,500, Ricoh's RDC-i700, which is expected to be out this month, requires a very compelling reason. That said, the i700 is a nifty device. A powerful 3.3-megapixel digital camera that's about the size of a videocassette, it flips open to reveal a high-resolution two-inch-by-two-inch touch-sensitive screen on which you can edit your photos. And its wireless capabilities enable you to surf the Web, send and receive e-mail, and post photos online.

CELL PHONE + MP3 PLAYER

What were they thinking? Teenagers love two things: chatting on the phone and listening to music. Let's unite their passions.

Greater than the sum of its parts? Almost, but not quite. If, like the Motorola cell phone/radio hybrid, the Samsung Uproar added music-playing capability to a cell phone without sacrificing anything, we'd probably have liked it. But the MP3 player drew too heavily on the battery, a serious issue for people who rely on their cell phones. And it took 15 minutes to download five songs using high-speed access. All that makes it hard to justify the Uproar's $399 price, despite some nice features.

DIGITAL CAMERA + POLAROID CAMERA (NO. 1)

What were they thinking? Take dozens of digital snapshots, choose and edit your favorite images and instantly print them on Polaroid film.

Greater than the sum of its parts? Close, but no. Everyone loves the instant gratification of Polaroid prints. But many of them prove to be mediocre shots, and the film can get expensive. In theory, the Olympus/Polaroid Camedia C-211 Zoom solves these problems because you print only shots you like. But the camera's size (as big as a hardcover book), weight (1.67 pounds) and price ($799) undermine a good idea. Chances are slim you'll want to lug it on vacation. It would be a lot of fun at a party or family gathering, but $799 is a lot for a limited-use camera.

DIGITAL CAMERA + POLAROID CAMERA (NO. 2)

What were they thinking? Some suckers will buy anything.

Greater than the sum of its parts? Not even close. Polaroid's iZone Digital & Instant Combo Camera ($100) is essentially two cameras--a rudimentary digital camera and a Polaroid--glued back to back. That means two flashes, two viewfinders and two shutter buttons, making it ludicrously confusing even to figure out how to hold it. Once you do, the bulky digital camera stores 18 low-res images but has no screen for previewing shots. The instant camera produces photo stickers roughly one-inch square--perfect for sealing up the box when you return it.

DIGITAL CAMERA + MP3 PLAYER

What were they thinking? You can listen to music while taking pictures.

Greater than the sum of its parts? No way. Does anyone really feel the need to listen to tunes between taking photos? Even if you're one of the six readers who answered in the affirmative, we feel that both Polaroid's PhotoMAX ($250) and Samsung's Digimax ($290) blend seriously flawed components.