I got one for my shimano c50. As long as you give accurate information to the guy and follow the instructions carefully, you can get a good fit.
I’ve knocked 30 seconds off my 10 mile PB this season. Whether that’s the skin suit, the disc cover, or Trainer Road, who knows - but something worked!
I use a disc cover but haven’t done any reliable testing (I did some poor aero testing with inconclusive results) to see how fast it is. It seems to work well though it lacks the normal wooshing you get from a disc.
I’ve heard the TR crew mention this before — if you can put your skinsuit on by yourself, it’s too big. It takes two, baby. 
Usually yes, standard rule is if can stand up straight without discomfort then too big…however in contact with nopinz guys who make trip suits and they say important to get ‘right fit’ not too tight as if stretched too much then trips don’t work and material doesn’t function as it should so actually less aero. But certainly want no wrinkles
What about tires?
The new GP5000 are super aero and have better rolling resistance than the 4000s. Lots of watts to be gained there…
I had a pair from Wheelbuilder years and years ago and eventually threw them out. Save your money for the real thing. They just aren’t that durable and I found snapping two pieces of plastic to a nice set of wheels then using electrical tape to seal the plastic to the rim silly. You have to snap them together just so or else the plastic will get wavy rather than smooth. Unless the road was uber smooth (so never) they sounded like hitting a plastic pool with a hammer. Very distracting.
I’d spend any leftover money on fast tires myself. If you save some money a HED disc is half the cost of a Zipp, ENVE etc…and tests every bit as good.
How aero they are will depend largely on the rims they are mounted on.
Actually, for some reason, the tread pattern itself on the GP4000 is very aerodynamic compared to other tires. I don’t think Continental ever intended for the tread to function in that manner, but its a happy accident. There are obviously a lot of factors involved, but GP4000s have been proven to be very fast in a lot of different contexts.
The GP5000 uses this same tread pattern, but has much better rolling resistance.
I got some and have only tried them once, they look great but didn’t really give me any extra speed hat I could notice.
Downside for me is the electrical tape was always coming loose and it took a while to get them sitting right. Now they’re stuck on with gorilla tape and look like a bodge job.
Pic is with electrical tape
Of the three tyres tested by Aerocoach the GP5000 was the one that inflated to the narrowest width so it’s no surprise that it tested as the most aerodynamic of the three. There are tyres both narrower and with better CRR if you so choose if they fit the profile of your wheels. According to that study the GP 4000 still tests as more aerodynamic up to 5deg yaw on the rim they tested on than the GP5000 and as a TT rider you are typically going to see fairly low yaw angles at racing speeds.
For a tyre/ rim combination to the optimally aerodynamic the rim should be no more than 105% of the width of the tyre (measured actually inflated rather than the advertised width!) so none of the combinations they tested may be optimal. While the GP5000 may be a good tyre it is also highly dependent on the wheelset you own there might be better options.
https://silca.cc/blogs/journal/part-5-tire-pressure-and-aerodynamics
