I have that flash. Works well. I bought it specifically for the greater zoom range than my Canon 580EX. I've used it in the rain a few times.
I think with some 3rd party flash the focus assist is not as good as Canon, ie the red grid pattern is not quite as good as the Canon. I use mine outdoors at long range so have not checked that. You can at least search for info regarding that aspect. I like the audio indications of this particular flash better than the Canon.
It was about 1/3rd the cost of a Canon 600 and as I use it in the bush at night there is greater chance of me damaging the flash so it seemed a good choice. (A friend who is often with me has ripped the shoes off 3 of his Canon flash)
I have probably used it for several thousand shots, once it did not fire. That was one of the first few outings with it and I had probably bumped it so it was not aligned with the contacts on my Camera's hot shoe.
I've already posted this in the Canon 100-400 II thread, an example of what I use it for:
