I've never been a fan of glass-top humis from an aesthetic standpoint, and the homebrewer in me thinks light is the most evil thing on earth.

If you really want glass, though, don't cheap out. I would think the weakest point of a glass humi would be the point there the glass meets wood. If you don't have a good seal there, you will have many humidity problems.

Of course, I also suggest the heartfelt humidity beads. They do an amazing job of maintaining perfect humidity.