Re: P.v.a. Versus Primers......
I think it depends entirely on the surface you're sticking to and what you're sticking to it. There must be a reason that every single manufacturer says that PVA isn't suitable, I mean I'm sure they're not sitting round a table (In an evil lab) saying lets lie to all the tilers out there. They all say the same reasons as well, reactivates with water, sits on the surface, not strong enough.
I mean epoxy primer seems to sit on the surface but defo gives a strong enough bond, perhaps we should just believe all the people in the industry, tile manufacturers, adhesive manufacturers, tilers, chemists and except that tiling needs some specialist products.
You never know these chemists could devise products that allow tiling in every room of the house rather than just solid floors and walls.