@Revvy - I have not pressure tested them, I suppose this first bottling if they hold carbonation will be the test. I don't imagine them having a problem, however I don't have a lot of experience with brewing and carbonating.
@Connoryis - That is essentially exactly what I did, for these I normally use a transparent celadon glaze as a liner, pour into them, swirl, dump out. It should line completely but that was one of my concerns because if it doesn't that would be problematic as it is a stoneware bodied clay that would soak in liquid without glaze. I think my next flip top bottle project might be with a porcelain clay, then I wouldn't have to worry as the clay body would be non-vitreous after firing.
I will keep an update, and post better photos .