When I was holding one in John Lewis, a bloke actually came up to me and said:
"sorry to bother you, but we bought one of them and it was a total waste of money."
so we didn't buy one, and it turned out we didn't need one at all. We didn't buy a baby bath either, just bathe DD in the big tub, right from the start. If both DH and I are at home then she comes in with one of us.
People do really vary as I know some swear by the seats (as above!), but depending on your confidence/ other kids/ back strength/ feelings about co-bathing etc. it is perfectly possibly to put it on the list of "things they try to flog me I might not need". And save your cash.