we had one for Scout and I loved it. He was sitting quite happily by about 5 months so I found it the best option for us. I like the fact if he was to get the wobbles he was still kept upright and I didnt have to worry about holding on to a slippery baby.
Now he is a bit older I dont put alot of water in the bath anyway so I never had the problem of not having much water to cover him.
Maybe just make his bath a little deeper so he is sitting in waist deep instead keeping him a little warmer.
Just before you take him out lay him down to give his bum and willy a wash properly. Its ok to handle a wet wriggly baby for a short time so I really recommend the seats.