Among many BM products, model 42 (and 43, 47 also) is the smoothest in terms of less friction. As it has no pressure on to the blade by locking mechanism, zero or minimum friction between blade and handle.
Axis lock or Rolling lock systems come close. You can pull locking pin of Axic lock, or you can pull locking lever of Rolling lock to smooth out all the friction. Liner lock will not allow such kind of trick, neither do frame locks.
In spite of my love for balisongs, I love to feel the well precised tooling on folding knife mechanism that gives an "adequate" friction into the knife.