I've used them and although some of what was posted is true, with some thought the wheels are good, durable training wheels.
There are many versions of the Rev-X, and I'm not talking the Extralight, Ultrastiff, and Regular. The early versions had problems with the two sets of 4 spokes moving inward on the hub. On the earliest versions you could see the carbon fiber on the hub (i.e. about vertical to the spokes). You should not use these.
The next version had an aluminum cap on the carbon and (I think) circlips holding the aluminum caps in place. The center of the hub was noticeably narrower than the caps which sat just inside the spokes. These wheels are okay but not great.
The final version (and the one that was available in the different "models") had a center spacer which was about the same diameter as the caps on top of the carbon. The hub appeared to be about the same diameter between the spokes. I've used this wheel and it's been very reliable.
There are three variations plus the X-Braces.
Regular - regular wheel.
Ultra light - Ti axle, drilled out rim. Lighter but more flexible.
Ultra stiff - double layer carbon on the spokes, otherwise a Regular. Very stiff, not too much heavier.
X-Braces - these plastic things (H-shaped) sat between the spokes, with the vertical part of the "H" stuck to the spokes and the horizontal part being the brace. An I-beam on its side. They really stiffened up the wheel and I recommend them for any type of Rev-X.
Rev-X's are discontinued and my understanding is that there is NO service or warranty work available. My understanding is that many of the staff don't even know about these wheels.
If the wheel was crashed, all bets are off. You wouldn't trust a crashed regular wheel, you shouldn't trust a crashed Rev-X.
If the carbon is intact, the rim good, and there are no noises coming from the wheel (clacking or similar sharp noises) then you are probably good. Clacking or similar noises may indicate delamination of carbon from something else (carbon or aluminum) so the wheel should not be ridden. It could also be a loose X-Brace.
The wheels emit a fft-fft-fft noise as each spoke goes by. With high pressure tires, you get some tire "singing".
They are worth perhaps 2 mph at 30 mph.
Since they are pretty strong, they are good for commuting.
Since they catch a lot of wind, I would NOT recommend a front wheel for riding in windy conditions.
The wheels do not define a racing wheel category so they are not that popular. They are heavier than the light wheels and are less aero than the aero wheels.
hope this helps
(previous owner of perhaps 4-5 sets of Rev-X wheels, down to one SS Front)