Obviously inadequate for horizontal dropouts, but they work fine for either fork ends or vertical dropouts. These are widely used, at least partially because they're cheaper than internal-cam QRs, but I'm unaware of a rash of wheels flying off, despite the pessimistic predictions of some crusty traditionalists. The problem in this instance was that the QR was simply too loose and ground away at the dropout material. This was user error and would have been the case with any sort of QR.