It will bring your R9 down to 45 degrees. I have 10 on order.
Yes I've seen the reviews but they haven't put them under as much stress as mining and the 290 is vulnerable to throttling one the vrm heats up.
I may just order one to have a play with. I'm pretty small scale and live in a small apartment so heat and noise are very important. Stock 290 can be had for just over $400 2nd hand in Aus and there are plenty of used closed loop water coolers around.