These are much MUCH harder to put on that is suggested and it took me ages. I thought there was no way they would go on, though I managed it. They need to be stretched FAR more than you would think. The inner 'ring' that needs to slide into the headphones basically needs to be stretched over the entire headphone then worked back in with a thin tool (e.g. a blunt knife edge), and they ripped slightly but I think not to any extent that it will shorten their life.
Quality seems fine but the fitting is tricky, though Sennheiser's design for these is probably very much to blame, there must be much easier ways to design pad replacement.