No flex that I can notice unlock my stock cranks. Strong as all hell, I'm 180lbs and ride them almost all day every day doing stair sets and everything. They don't even creak. Also, they're light.
Nothing at all. Unless you like to have a rainbow bike, in that case the lack of colors may disappoint.
Everybody says that they're super hard to put on and blah blah blah. Put a little grease on the spindle, and the splines of the crank arm and it just glides on nicely. Seriously. I take these off and give everything a good cleaning 3 times a month and they're still easy to put on without any trouble.
Also, to the people saying the logo by your leg rubs off - I've been riding these for months and it's still there, clean and visible as day 1.
10/10 I'd put my feet on these any day. I recommend them to everyone who says they need new cranks.