I've just had a Krentz endpin installed, so I thought I'd chime in. Yes, it really does affect the sound of my instrument for the better, and yes there's really a difference between the two knobs. In general, I feel like the best part of the endpin is not the two knobs (although they are great), but the material it's made of. They say it barely absorbs vibration at all, and I can really feel that the body of the cello is now more resonant. Even the hard wolf I've had from e flat to f has now mellowed down.

It fits just as any normal endpin, you just have to choose which knob you're most likely to use more often and put that on the side of your dominant hand. It takes a while to get used to the turning mechanism, there's a specific way in which the knobs alternate, so there's the initial fun of tightening both knobs and having the endpin still loose. But it only takes a little while to get used to it.