WUCV has probably gone ahead and made a purchase - but I'll leave this comment as a warning/recommendation for other potential buyers.

I had a similar experience to Sean - I got a YN-565EX back when they first came out. I was tempted by the low prince - needed a more powerful flash and everyone raved about them. It worked quite well for exactly one year. Then one day when doing a paying gig - it stopped working. Luckily - I had my good old 420EX with me. It saved the day. It turns out the Yongnuo just plain old decides to work one day, and not to another. I would never have found out except after I threw it in the closet in disgust I accidentally grabbed it when I went out on a shoot - and was shocked to see my mistake. For some reason it worked, and stopped again a few days later.

I've since gotten 2 600EX-RT's. Couldn't be happier. That said - Yongnuo's physical build is excellent, and nearly identical to Canon (hence my grabbing the wrong flash!).

And, I myself have purchased a YN-E3-RT. Call me nuts, but there's a little bit less going on as far as electronics than a flash - and I really liked the idea of having the AF assist and firmware updates. The AF assist is really something that Canon needs to add. I've had it since December, and it has worked flawlessly.

You really have to consider it as a gamble. Although Yongnuo is supposed to have improved, they have absolutely no consumer support infrastructure in place. If your product dies - even if it's one with a warranty (and many of their products have none!) return to your seller (follow Sean's advice!) or if it's too late, send off to China and wait for a couple of months to see what they do. $150 is really nothing to sneeze at, and for a little more you can have the Canon. Or, look for the times when it's being bundled with a 600EX or two, and grab it. So far I'm happy, but I haven't hit that magic 12 month mark! The build is nearly identical to Canon, and of course the menu functions are exactly the same. I'm one of 2 reviews on Amazon, so you can see my thoughts as I sat with the Canon and did a side-by-side comparison.

P.S., after 8 or more years, the little 420EX still works fine!