Wilt wrote in post #18327864
One way to look at the question...
At 1/7 the price of a 600EX, you can afford to throw away 7 failed units for the price of purchasing the Canon flash!

And who is to say that the Canon flash wouldn't fail? Things do; nothing's perfect - all you are looking at is the Balance of Probability. The way I look at this is that the likelihood of 7 consecutive Yongnuo flashes ALL failing is fairly slender.
Another point is that we rarely get the full story of these failures. When was the last time you came across someone saying "Well, I've dropped it a few times and it's blown over on top of an 8ft lightstand twice. It lives in the back of the car where it's subjected to really wide temperature ranges and rattles about taking little knocks all day, every day. Then it suddenly went and broke on me so they're all totally unreliable"? Doesn't happen, does it - all we get is "They're rubbish ... totally unreliable ... avoid". 
Final point - at the low price point of the unit, replacement with a newer model of higher specification is far less painful than with the higher priced Canon unit. I have 2 Metz 45 CL4 (pre-digital models, no less) hammerhead flashes which are probably older than half the members here (1970s/80s??). Ultra solid, ultra reliable (never even needed a replacement tube), seriously expensive (back then - may be worth as much as €1 / £1 / $1 each now
) and I still use them but there is so much that they DON'T do - no TTL let alone ETTL / no zoom reflector / no 2nd curtain sync / no HSS / s..l..o..w recycling / replacement battery packs cost as much as a full new YN flash (but I build my own anyway). Very very good units but unbelievably outdated and limited by comparison with modern units. If I'd been stuck with those because of the money invested there'd be so much I couldn't do. Far better to have the flexibility of updating without the pain of discarding.
Of course you could buy the Canon unit, but it doesn't really actually guarantee anything at all. BTW I have 4 (old) Metz, 4 Godox, 4 Yongnuo but ZERO Canon flash units - but those were my choices.
Failures over the last 50+ years mainly professional use (wrinkly old pensioner now living on the proceeds of what the flashes produced over the decades)?
1 smaller Metz (54MZ4) needed a new tube, nothing else apart from the inevitable batteries. So my single failure was on a (then) top-of-the-range flash, not a cheapo.