This sounds interesting - thanks for this post.
My ILLUMI Acquashield is better than the previous PLESON, but both are TPU and therefore a bit rubbery and not the best for using the stylus. The ILLUMI does install perfectly, and the edges stay down even with my minimal case.
But, the rubbery surface leaves imprints of what I write. Then, once the surface is uneven from my writing, when I write over that area the Spen touch becomes intermittent over the uneven surface. I'd really like a harder surface.