I've been using these for the past year, here's my quick experience/review for whoever's interested.
I've used these as part of a hobby-grade studio-in-a-bag setup with a bunch of 603's (six total, I have two camera bodies) and four Yongnuo manual flashes.
They're manual-based radio triggers, much similar to the pocketwizards, these are NOT ETTL devices. You set your flash in manual mode with a power level, or attach them to strobes.
The only signal these send is to pop, there's no ratios, or exposure information passed.
Within that context, these have worked GREAT.
They use AAA batteries, not the lithium cell batteries (CRxxxx) or the 123 batteries. I use low-self-discharge batteries (like Eneloops), so they're always ready to go. They're easy on power, and in an emergency, you just have to find AAA's, not some weird photo or cell battery.
They broadcast on 2.4GHz, and the first thing I did was set a different channel in case I came near somebody who didn't bother. I have never had a misfire that wasn't related to the flash not being charged.
These are transceivers, meaning that they transmit and receive, so there's a hotshoe below the unit that's meant to mount on the camera and receive the trigger, as well as a hotshot receptacle on top that's meant for mounting the flash. There's also a PC plug onboard that you can use to trigger to the larger strobes. These are cool in that you just grab one, and use it on a camera or flash, doesn't matter which.
The transceiver will pass-through and fire a manual flash attached onto your camera through the unit, however I'm not sure about the ETTL part of it. Works fine for a manual flash tho for when you want a fill or such.
There's no lock for the hotshoe foot on these. That's my largest gripe on the 603's, is that if you use a non-clamping attachment (such as the "foot" that comes with most flashes) or use it with a flash on top of it on your camera, it will NOT be secure. You can keep a handful of rubberbands for this "just in case". It'll be fine while it's level or steady, but when you pick it up to move it, the foot will fall out. If you have a 603+flash on your camera body, beware, it'll fall off!! These are very light and stay attached just fine on a camera if you don't have a flash on top of it.
There's a separate plug for the remote shutter operation as well. Here's the rub on that one though, you have to have it mounted on a hotshoe for it to work, it's a little annoying. But, no biggie. I only use them for manual flash work.
These are really great units, they're available for very cheap in a two-pack on eBay, much much cheaper than the pocketwizards. The only reason I'd move to the pocketwizards, would be for the group capabilities... these cheapos only work on a broadcast, every trigger operates at once, no groups.
Overall I love these, they're a LOT cheaper than pocketwizards, and I have found them to be just as reliable, plus they're transceivers, so you don't have to worry about what gets used where, just use them and go.
Hope that helps!
