Dear @best-groove : I own 3 of them and certainly is way different to a reflex clamp that can’t makes what the 666 makes, I own too reflex clamps.
The 666 should last around 25-30 minutes. Time to time you have to clean the perimeter rubber with the like leather square cloth that comes with and you have to be sure that the LP side that looks ( face down. ) to the 666 is clean to avoid that dust be " clamped " to the perimeter rubber. I own a manual air pump and the battery powered one that sometimes does not works as we need it but you can use any air pump for that task.
Now, 7-8 minutes is way low time and you have to check this: the perimeter rubber is holding by a nylon tiny ( like a lasso. ) around all the inner perimeter of the rubber that hold the LP. That’s that you have to take the 666 in your hands and seen at the center perimeter 666 edge if that nylon " part " is still there around all the inner rubber perimeter. Trogth the time that piece of nylon could be broken and then happens what you are experienced but with out have in my hands I can’t help you in better way.
maybe some one can " translate " what I posted due that my english vocabulrary is not adequated.
Btw, the 666 makes a difference for the better.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.