Just noticed this thread, I’ve got tempered glass protectors on my 5 and 6+, just ones I found on eBay for a couple of quid, and they’re brilliant, really slick to the touch, possibly even more so than the original, vastly superior to plastic ones.
The trick to positioning them, because they really are slippery, is to run a strip of masking tape or duct tape along one edge, get the protector lined up exactly, then rub the tape down around the phone body, so it’s hinged, then make sure there’s no specs of dust at all, and then, with the protector at an angle above the screen, pull the protective film off, away from the hinged edge. This stops bits of dust having a chance to settle before the protector is in place.
It’s almost impossible to tell my two have anything on them, other than the fact the 6+ one doesn’t quite go all the way across, because of the curved edges.