I was thinking more along the lines of those made by Fred Wissen (ptownsubbie) and others which are much more substantial. I didn't realize that purpose built blank molds that flimsy even existed.
I think there has always been some concern that using silicone under pressure somehow changes things--like the pressure will somehow cause the silicone to deform and somehow ruin the casting. Unless there are bubbles in the silicone, it ain't gonna happen. If you can get the pour into the pot intact, it's going to survive intact. In short, the pressure pot should not have any effect--although I'm willing to be corrected subject to experience.
Seems that this question has come up every couple of years or so.
Bill