It doesn't blunt the blade - it's the paper and card that blunt blades - after all, you don't actually use the blade on the glass, huh. The self heal mats are great, but this is for me, a step up. No healing to be done for sure, and occasionally my teenier projects slide when I'm cutting...because I've not allowed room to hold them. But the glass doesn't absorb the energy that I put into cutting like the self healing mat does - the blade will never stick in the mat and the cutting is therefore a bit easier I think.
As for breaking it..well I dunno, I think you'd have to go some; it's tempered obviously, and I use it as my heat gun base too - although sometimes that causes condensation on the mat surface which is a minor annoyance. It sits on my desk, and once a month it gets passed to my tote for transport to a crop and back. That's not to say that I haven't dropped it, but it's hasn't been from desk height, and I can't say if it's landed flat or on a corner - these things happen so fast!!
I like the grid - I occasionally remember to use it for lining straight stuff up too! So there you have it, my glass mat and thoughts thereon. The best use this glass mat has is that it forms the border/barrier of use-able space on my desk. I can see that once the mat is covered in stuff, the whole desk top needs to be sorted, So it's a closet barometer too!
I'm not a snob about it - I use it and love it, I don't mind if you've got a self healing mat and love it, there's no tool-up-man-ship here, this 'review' is just doing what I do best - talking about myself!