I'm looking for a simple hot shoe flash for my 10D. I don't do complex photography requireing multiple flashes with master and slave, etc.

550 has 55 meters guide number while the 430 has 43 meters.

For majority of casual users, 430 should be more than enough.

I'm not sure aboth the actual specs, but I suspect the 430 has shorter recycling times than the older generation 550.

430 is also smaller, which is especially noticeable with a smaller camera like 10D

works wonders when you know what you're doing with it- especially indoors.

Outdoors, the reach isn't that great, but then I had it on at night/dawn trying to photograph animals at distance.