They're brilliant. I always found the bedside cot a half way house between co-sleeping and getting up to feed (I've done both). For a while I sat up to feed but always put DS back into his cot when he went off back to sleep.
If you're BF, definitely definitely worth it (it sucks getting out of bed to feed) Just have your cushions or whatever close by, and you're sorted. (I had a big squishy one the went along the foot of the bed when not in use)