I have never put DD in one because EVERYONE (just about) tells you how bad they are. They can be dangerous because of slippery surfaces or stairs. The kids can also go really fast and bang into things. They are also bad for their legs if in them for long periods.

DD had a lend of an exercaucer for about 3 months in which she would "stand" for about 10 mins everyday and play with the surrounding toys. She really liked it because it was a diff perspective on the world but it couldn't move.