I've used the Zagg protectors for years.  I used the glass protectors on my iPhone 6 plus.  I had to replace it about 5 times over the past year due to cracks in the glass and chipped edges.  This did not occur due to drops or mistreatment of the phone.
By the way, I spoke to someone at the Zagg kiosk and they said the current glass protectors work fine with the new 6s models.  But I am hoping that Zagg comes out with a thinner, more durable glass protecter.
I am also looking for another type of protector for my 6s plus.  Something that is thinner than 0.4mm and perhaps is curved to accommodate the curved iPhone screen.  Still searching......