I wondered why flip-top playfield glasses didn't catch on & become mainstream. Sure, pins weren't exactly designed to be in the home where there might not be room in front of it to slide a glass out, but hey.
So there's the advantages:
1. no room needed in front of the pin to slide out the glass
2. No 2nd person needed to hold the glass out.
3. Reduced chance of glass "explosions"(could be wrong on this one)
4. No need to place it carefully elsewhere while you're working on/under the PF
Disadvantages:
1. Parts cost
2. Car hood "slam" could cause an explosion(shock absorbers like on toilet seats?)
3. Clearance problems when trying to pull out a playfield on more complex machines?
4. Increased diffy on replacing pf glass, unless it can be slid out from the upper/lower rails with a bit of unbolting.
5. Need to redesign hinges to lower the backbox
6. need to implement design where the backbox & flip-top can't sandwich into each other.
To me, it seems like it's a better bang for your buck to implement compared to pf toys, toppers, etc.