Just mounted a H600. I'm not one to cuss a lot but this cooler made me cuss for over an hour. No other cooler, liquid or air, has caused me the problems this one did.
The glaring issue is that the screws which go through the back (and backplate) are so ridiculously short, that you cannot mount the pump block onto them even loosely before placing the front screws and tightening. Because of this, you kind of need 3 hands, or TIM application will be a mess, and good luck even getting it fitted. It's like pin the tail on the donkey at times. You will do it, if you persevere, it's just not a pleasant experience.
If long enough back screws were provided (as other brands do), the pump block could be mounted loosely onto the back screws which holds it in place well enough for you to comfortably press and keep the back screws in position with one hand, and insert the front screws and tighten with your other hand. I cannot comprehend how whoever was responsible for the mounting system did not realize that. You don't want people hating the cooler before they've even fired the system up. I'll soften up a bit if it runs well when I fire it up. But I wanted to write this message while the iron is hot so you can see how it made me feel. Unadulterated feedback.
Serious - change those back screws fast, Antec.
Another thing I noted was that the H600 will unfortunately not be compatible on the rear of many cases that say they can take a 120mm rad on the rear. This is because the ends of the radiator are not rounded off on the edges like other coolers, but square. And the rivets in the upper rear corner of many cases will block the cooler from aligning with the screw-holes. This was the case with the H600 and the Corsair Carbide Spec 01. Good thing it fitted on the top. If you are building in cases that have a rear mount for a 140mm, you should be fine. And obviously there will also be some cases out there that don't have that pesky rivet (or made sure to trim it as much as possible on the inside). Otherwise be prepared to remove the rivet if you want the cooler on the rear.
And finally, the spring mechanism on the long front screws... they never feel taught at any moment. They leave you wondering if it's taught enough, or not. Just no way to tell. You keep turning the screws and eventually just get tired of it and stop. Even with a spring mechanism, the builder should be able to "feel" when it's the right time to stop.
On the bright side, the quality of the fins etc is super. I've seen other coolers with bent fins all over the place.
Will add a bit more to this post tomorrow when I get it running.
EDIT:
Liking this cooler a lot more now. It just looks good, sounds good and works good.
@ stock clocks Vcore 1.23-1.24, stock fan, Arctic MX4 paste - i7-6700K
Cinebench - 45C
Realbench 2.43 - 49C
So this thing is very impressive cooling-wise. Temperature-wise has substantially more overclocking headroom than I expected. The pump running at over 3,000 RPM must help, I imagine (and it's not noisy). The stock fan has a noise to it, but not unpleasant and nowhere near the jet-engine noise of some other AIO stock fans on load. Great value for money. All in all, this makes up for the shoddy mounting system, which I hope they can improve upon, as I would want to use this cooler in future builds.