These HDGlass protectors are very expensive, but worth it in the long run when spending close to $1000+ on a device. I bought this last year (April 2016) and a couple months using it, I accidentally dropped my Surface Pen on the edge of the protector and it cracked (just a tiny round, ~6mm, crack). The protector was still usable, so I kept it on. However, when I removed my UAG case, it somehow bent the glass screen, and a huge hair line crack occurred (manly because of the small crack from the pen dropping on it). Now, protector is still usable, but I decided to RMA it a couple days ago for another. Zagg warranty is amazing, especially with lifetime warranty. Just pay $5.99 shipping, and then send back the bad one.
Now for the downside. This protector is VERY THICK. I found myself very annoyed over the past year because I use my Surface Pro 4 for School (Nursing). I use OneNote, and it was very hard to "pinch-to-zoom" and scroll. Also, some finger strokes wouldn't register, causing me to repeat the gestures, which was very irritating. Because I didn't use the SP4 much without the protector when I first got it, I assumed that it was just the hardware being slow and unresponsive. That isn't the case. This screen protector is what causes the screen to be unresponsive. I have no issues without the screen protector, but since I RMA'd it, I will re-add it just to protect it more.
I highly recommend this screen protect if taking the SP4 out of the house where there's a possibility of dropping it.