(See updated notes at bottom!)

First off, awesome idea!

Unfortunately, the idea wasn't perfected.

Getting your camera off the flash has gotten MUCH easier over the years - wireless triggers, ETTL cables, hotshoe-slaves, PC-Sync cables, you name it.

The problem is getting that flash to carry ETTL wirelessly. So far only a few transmitters do it, and they're all VERY expensive (requiring not only a transmitter, but also a receiver for each flash). That's where this little guy steps in.

The STE2 pops in your hotshoe and wirelessly triggers your Canon flashes (with slaves). The first problem here, is the "Canon" part - unlike the other options which work with ANY brand of flash, this one works with the Canon system. If you only own Canon flashes, no problem! If you own a mix, you've got a problem (the Canon's don't come cheap!)

The next problem is that it's line of sight based. This means it has to be able to "see" the other flashes. Not so much of a problem indoors (it'll bounce off walls and generally hit the flash), but outdoors you'll have issues. Sunlight, especially, causes signal loss and (especially using multiple flashes) it's not something you want to have to rely on (you'll spend time either trying to correct it, making sacrifices or not notice that half your flashes didn't fire (which would be too late)).

If you already own a Master/Slave flash (like some canon 580EXII's), try that on wireless mode to see how well it works outdoors, that should give you an idea of what to expect from this. Unfortunately, with it being unreliable, I just can't recommend it for anyone planning to use it outdoors. Indoors, you should be fine, but is it the option you need or would a cheap transmitter or sync cable do the same job for you?

Next problem is the battery - for some odd reason I can't understand, they decided to use non-standard batteries. No AA or 9V here, we've got a "2CR5" here. Have a bunch of these lying around? Chances are you don't, and  you'll want spares for when you need to replace it!

One very cool thing about it is that it has Focus Assist - that's the little red pattern that the canon flashes use to help you focus in low-light situations. If you don't need to use the flash, you can still use this thing to help focus in darker locations without needing to mount a high-flash on top. I know I've used my 580EXII as a focus-assist tool (not using the flash output), so having this (much smaller) option is very nice. The question is, is it worth the asking price? For me, I say no. For you, maybe it is.

There are much better options out there - if you just need wireless, pick up a transmitter/receiver combo for 1/10th the price of this. If you need ETTL, spend 1.5x the price of this and get one of the new pocketwizards and a receiver - the extra range (and not having to fight with getting a line-of-sight) is worth it in the long run.

--UPDATE 11/15/2010

A 3rd party manufacturer, Yongnuo, has since released their version of the ST-E2 transmitter. Costing a bit less than the Canon model, it's nearly identical but with some improvements (including longer range (Autofocus assist beam and transmitter beam, ability to swivel left/right, runs of 2 AA batteries). While still not perfect, the Yongnuo version is a considerable improvement and one I can actually recommend if you're using ETTL!
(See updated notes at bottom! )

First off, awesome idea! Unfortunately, the idea wasn't perfected. Getting your camera off the flash has gotten MUCH easier over the years - wireless triggers, ETTL cables, hotshoe-slaves, PC-Sync cables, you name it. The problem is getting that flash to carry ETTL wirelessly. So far only a few transmitters do it, and they're all VERY expensive (requiring not only a transmitter, but also a receiver for each flash). That's where this little guy steps in. The STE2 pops in your hotshoe and wirelessly triggers your Canon flashes (with slaves). The first problem here, is the "Canon" part - unlike the other options which work with ANY brand of flash, this one works with the Canon system. If you only own Canon flashes, no problem! If you own a mix, you've got a problem (the Canon's don't come cheap! )

The next problem is that it's line of sight based. This means it has to be able to "see" the other flashes. Not so much of a problem indoors (it'll bounce off walls and generally hit the flash), but outdoors you'll have issues. Sunlight, especially, causes signal loss and (especially using multiple flashes) it's not something you want to have to rely on (you'll spend time either trying to correct it, making sacrifices or not notice that half your flashes didn't fire (which would be too late)). If you already own a Master/Slave flash (like some canon 580EXII's), try that on wireless mode to see how well it works outdoors, that should give you an idea of what to expect from this. Unfortunately, with it being unreliable, I just can't recommend it for anyone planning to use it outdoors. Indoors, you should be fine, but is it the option you need or would a cheap transmitter or sync cable do the same job for you? Next problem is the battery - for some odd reason I can't understand, they decided to use non-standard batteries. No AA or 9V here, we've got a "2CR5" here. Have a bunch of these lying around? Chances are you don't, and  you'll want spares for when you need to replace it! One very cool thing about it is that it has Focus Assist - that's the little red pattern that the canon flashes use to help you focus in low-light situations. If you don't need to use the flash, you can still use this thing to help focus in darker locations without needing to mount a high-flash on top. I know I've used my 580EXII as a focus-assist tool (not using the flash output), so having this (much smaller) option is very nice. The question is, is it worth the asking price? For me, I say no. For you, maybe it is. There are much better options out there - if you just need wireless, pick up a transmitter/receiver combo for 1/10th the price of this. If you need ETTL, spend 1. 5x the price of this and get one of the new pocketwizards and a receiver - the extra range (and not having to fight with getting a line-of-sight) is worth it in the long run. --UPDATE 11/15/2010

A 3rd party manufacturer, Yongnuo, has since released their version of the ST-E2 transmitter. Costing a bit less than the Canon model, it's nearly identical but with some improvements (including longer range (Autofocus assist beam and transmitter beam, ability to swivel left/right, runs of 2 AA batteries). While still not perfect, the Yongnuo version is a considerable improvement and one I can actually recommend if you're using ETTL!