Flipping hate toilet seat fittings with a passion. The one's on our downstairs loo are a cheap generic fitting, and I've only replaced one part of it in 25 years - that's been great. Not the same for the upstair's loo which has had umpteen fancy loo seats, all for the fittings to fail. Current seat has been fine though for over 4 years FINALLY.
Caravan loo has been a pain for a long time - rusted on. One side finally broke this year, and I'll admit, I got 'hulky' with the other side and just wriggled it until the fitting broke and hack sawed off the last bit. New seat installed, and it had a plastic expanding wedge arrangement (similar to OP's) that actually works well.