My Hama record clamp arrived today (with a record I <cough>had</cough> to buy to take the cost over the free postage threshold.
Once on it works well. It works by clamping the spindle rather than by weight. It's actually quite light, which I like ... but:
It takes too much downward pressure to put on, on my LP12, and I can't apply it while the disk is spinning as that results in a lot of complaining noises from the belt.
So I think it may well be a very good solution for unsprung decks, especially direct drive ones, but not for sprung belt drive decks.
Thanks Kev (scotty67) for the heads up. Definitely worth the punt.