We used one for DD and it worked out great. She used it until she was almost a year old. DS seemed to think it was a great surface for pushing up on, so I just got a non-slip bath mat for the big tub. But if I could use the inflatable one with him, I would!
(The bath mat we are using is the IKEA one that is shaped like an alligator, if anyone is interested. Amazon also sells it).