The Bessy UniKlamps are a cheaper (but lighter duty) version of the K's. They're not as smooth as the K's but I couldn't justify the price of the K's when I bought them.
Despite their limitations I love them and they've become my "go to" clamps. The large parallel jaws and decent holding force make them useful in all sorts of situations. I wish all of my other clamps were as good as them - but then I don't own any of the other premium brands.