They do glass. I had it done when they first came out. The install is extremely accurate. The version of the glass protector they use for the machine install has VERY close tolerances to the home button and speaker which is nice. Also, the glass is very thin which I liked also.
Now for the bad news. None of the edges are smooth and rounded which makes the protector much more noticeable to the feel than screen protectors twice as thick (especially regarding the home button cutout). Next, The screen protector scratches VERY easily. I had mine on for 3 months and in that time it had more scuffs and scratches than a sp I've had on for over a year previously. Also, the oleophobic coating was worn away in areas of the screen that I swipe a lot.
They do have a lifetime warranty and when I contacted them they sent a replacement with a self install alignment frame. Apple will not do a machine replacement for warranty situations unless its within Apples return window.
I never installed the replacement as I moved on to an edge to edge screen protector. Maybe they have changed their production line quality. I would be curious if the most recent installs have these same issues.