I bought 6 glass cats for my tank and they are awesome!!
They do prefer to hang out behind a large rock but they start to come out around 7pm and browse around. I will agree that they go crazy at feeding time, it's fun to watch!
I was worried about how picky they were going to be with food, as I read that they won't take anything except live and maybe freeze dried foods because they are captured out of the wild.
For the record, they willingly eat freeze dried daphnia, blood worms, krill AND pressed fish pellets and flakes no problem.
At first they appeared to have no colour because they are "see-through" but they actually have a pearlescent shimmer to them in the light!