I had been preparing my "old" iMac to give it to my church for the bookstore and had wiped the HD, installed all new software and was ready to deliver it. I set it down on a bench and the cushion slowly squished down, dumping the computer on its screen. Fortunately the LED screen was still OK, just the glass was broken. Instead of having to pay for the repair, I just bought the glass, the suction cups and went to work.
Mostly great. While trying to put in the new glass =I realized that one of the aligning pins had broken off in the case so I had to remove the front of the computer to get it out. A minor bump in the road, helped by videos on YouTube (I watched 3 different ones)
Take it slow, keep it clean and it isn't a difficult job.