I bought 2 of these about 1 month ago. Loads of posts on this. I read the posts like yours and am now careful not to over tighten – They have solved my squeaking problems and have had no problems with them – I think you can over tightnen them and tehn you risk mashing the plastic teeth. I put a bit of copper grease between teh handle and the locking washer which helps to undo it.
I have a spesh 9mm QR on an old front wheel and I think you can still order these though specialized from previous posts – you could also use a through bolt instead of a QR. I think you can get a 10mm from speccy as well.