I have had a Renzetti Presentation 3000 for 30 years now with exactly zero problems. None. Ever. It has the screw mechanism instead of the cam jaws. This picture is taken from the Renzetti website -
Why aren't there screw-type jaws made much any more? I also have an HMH with cam-lever jaws and the screw-type is much simpler and easier to use, at least to me. Obviously, I must be alone thinking this way.
Joe