Preferences friends?

I'm in need of new blocks for our lab, and before investing I'd like to learn more about pros/cons, perceptions and preferences you all may have. We're still stuck with an ancient manual AIT Speede blocker, and it uses the old metal half eye blocks (1682-A).

I have exactly 10 blocks. They're all old, and many are a bit worn from improper use by previous employees who didn't know how to deblock a lens properly. Needless to say, the wait to block up new jobs is hindered as I have to run others to free up blocks and keep the cycle going. But before I plunk down on more, I wonder if I should stay with the metal or move to plastic.

Any less chance of crazing w plastics? Any difference in terms of slippage?

Secondary to that, I'm also going to be reordering some new leap pads soon, and was looking at Dynamic Labs "ProGRIP II". I'd love to get away from constantly needing anti-slip discs in addition to pads. Any experience? Do you have a go-to pad you prefer that is as fail safe as could be hoped for?