Depends on the bike, the rider, and other factors. Not all folding bikes are the same. As MB1 said, plenty of people have done centuries and other demanding rides on quality machines like the Bike Friday Pocket Rocket.
Heavier? Heavier than some bikes, but lighter than a lot of them. Bike Friday says their Pocket Rocket Pro weighs under 20 pounds. I suspect the small frame and wheels make it more aero than a typical road racing bike. The riding position can exactly duplicate a normal bike. Obvously there are some handling differences, but these bikes are certainly made for and capable of such rides.
I'm not sure what the pro kit has to do with it.