Ok so Play pens - useful or a cruel form of incarceration?

I think I would like to get one for Charlie around christmas time - he's not mobile yet but there are going to be heaps of kids zt Christmas this year and they run around and scream and don't look where they're going - so I thought if I had a play pen thingo with Charlie in it, then instead of squashing him they'll just wind themselves....

Anyone got a play pen - if so what sort is it and do you like it?

Thanks, Em