I have a power support crystal on my iPhone at the moment, and i did have a little issue with installation of my slider with this screen protector on.
The problem was that the slider i bought had a slight bit of flesh about halfway down the case, which caught on the sides of the power support causing it to temporarily raise. All i had to do was open with slider up with a little pressure while it went over this bit and it was fine.
I've heard that the SGP steinheil crystal is super thin and therefore works very nicely with the slider, but i have never used or installed one of these so i dont know.