The cycling weekly link in post 2 above says a suit saves between 21 and 28 seconds on a 40K to at 25 mph. The data in Elvos post shows an even bigger gain. 25 mph is a good pace for a competitive amateur cyclist. In fact a nice measure of cycling fitness is a one hour tt. If you train hard, it’s difficult to get that kind of speed savings most other ways. So the cost of a suit might be worth it.