I have used literally dozens of these Cometic gasket sets over the years and the only problem I ever had was from a head bolt that I torqued up properly but was binding on its crankcase thread so wasn't doing its job!
I would be interested to know if you think you might have an issue with them
i dont think ttr steve would sell anything what was no good he and brian have tried and tested many spares over the years you will have no problems not like ebay once you have bought it from ebay thats your problem