Like everything, there are the pros and cons to each possibility. When I used my observation hive, it was with glass. Even with long use, it tends to stay clean and provide a cler view of what is going on inside. When cleaning is needed. no plastic, even plexiglass, cleans to a clear polish like glass.
So why don't I have an observation hive in use today, You can give one guess---
You got it! Glass breaks, plexiglass doesn't.