I have a Gamma starting clamp and one of the old Babolat starting clamps that is supposed to be so great. I will admit my Babolat is much harder to open and it has two spring where the Gamma has three. BUT, the Gamma has never slipped for me. How good is good enough. I will say this though I NEVER pull tension against a clamp with no tension on the other side of the clamp no matter what type clamp I am using.
I would like to apologize to anyone I have not offended. Please be patient I will get to you shortly.