M.K.
We used the exact same bathseat as Toni did in the full-size bathtub. No safety concerns on my part whatsoever -- as long as you never, ever leave his side (no more than an arm-length away), you'll be fine. I think the danger comes from people who kid themselves and think "he will be safe for 2 seconds while I grab a different towel."
My son was particularly ambitious and tried to stand while in it, but we used a very, serious voice to say "sit down, no standing" and physically sat him down again. He quickly learned that when we said that, he knew what he needed to do.