deh menwrote a review of Mercury Wheels M5 Clincher Wheelset on July 26, 2015
Familiarity: I've put it through the wringer
This is my first set of full carbon clinchers, so keep that in mind when reading this review. I got my set of Mercury M5s off this site on sale for $1000. After 1800 miles and a successful Spring racing season, I definitely feel like I have gotten my money's worth. These wheels are noticeably stiffer/less flexy than my 1550g aluminum clinchers (both my Rol Race SLs and my American Classic Victory 30 tubeless). This is very important to me as a 170+ lbs sprinter, because I am able to flex a lot of wheels and I find it annoying. I also feel like these wheel hold speed better than my 30mm aluminum clinchers, although I don't have a wind tunnel to verify it. As far as cross wind susceptibility is concerned these do get pushed lightly in the wind, but the feel is similar to my dad's HED Jet 6 FR wheelset (which is supposed to be pretty good in that regard). Many of the smaller riders I know prefer 35-48mm wheels because it is harder for them to control deep wheels, while I see a greater percentage of larger riders on deeper wheels.
I have had some issues with the wheels, and if I did not get them for so cheap (relative to other carbon clinchers) I may have given then a lower rating. First of all, I had to get the wheelset re-tensioned after delivery because it kept coming out of true. It's annoying that wasn't caught in the factory. Another "problem" is people are saying that the set weight is significantly higher than claimed. Manufacturers lie about weight all the time, but it's still annoying. Finally, you can only use Mercury's brakepads, which squeal and wear down too quickly. At least they have decent stopping power (comparable to Shimano pads on aluminum, but not as good as Kool Stop Salmons or Serfas triple compound pads).
Despite these problems, I do like this wheelset a lot for its stiffness, good looks, and aero benefit (or maybe it's placebo). Speaking of aero, an article I read in Velo showed the difference between the "best" aero wheelsets and the others (including old school narrow ones) is much less than the difference between an aero wheelset and a non aero wheelset. So you get like 90% aero benefit you would get with Zipp, HED, Enve, etc. I pulled that number out of thin air, but the point is the article reckoned there is little difference between most deep carbon clincher wheelsets.
Again, overall, I would recommend these wheels for $1000. My impression is that you are not going to get much more benefit by upgrading to a "better" wheelset for twice as much. It seems you get a significant aero and stiffness benefit for the price. If you have a little more money and/or these wheels are not on sale, another cheap, but good performing wheelset to consider is the November Rail 52 for $1385. The advantages to them are you get wind tunnel tested rims (with the drag sweeps are viewable on the website), high quality White Industries hubs, and they are pretty light at 1570g. That is the wheelset I had planned to buy (back when they were $1500) until I saw these on sale.