I have a Cinelli Super Corsa that I put a set of S&S couplings on and they indeed do stiffen up the frame. The couplings have a toothed interface that is compressed by a threaded collet that insures that they never come undone until you use the wrench to do so. I have had the bike up and running for over a year and can feel no difference in handling and it adds on the equivalent weight of an extra water bottle to the bike. The couplings are made out of stainless steel and are a very finely made piece of equipment. They allow the bike to be taken apart and I place the 2 halves in a bag along with the wheels and they transport to anywhere on public transportation where you just reassemble the bike and ride away with the bag over your shoulder. An elegant solution to traveling with your bike without going to the small wheeled folding bikes that are available.

Fixedgearhead