My lo has used a walker since just before 6 months, and she still LOVES it. Sjes crawls and cruises along furiniture now, but its still allows me some respite, because our living room is too small for a baby jail or travel cot, so it allows me somewhere safe to put her if I need to pop to the loo or do something!
She is soo fast in her walker now and follows me around the house in it!
I think if you are sensible about it and dont leave them in it for ages at a time, they are fab, as long as your lo likes being in it- which she does x