Hi,
About two months ago, I read a lot of reviews on different bath seats, and found three general complaints about them. First, not all seats appeared to be compatible with all bathtubs. Second, parents seemed to have trouble maneuvering a slippery baby in and out of the seat. Third, cleaning diaper parts was challenging.
I ended up choosing the "Inflatable Safety Duck Tub" by Munchkin (http://www.munchkin.com/products/detail.html?section=prod.... We started using it when our daughter was a little over 6 months and had graduated from the infant tub and the kitchen sink. At 8 months, we're still enjoying it. Most of the time, she lounges with her head on the duck's tail and I can use both hands to wash her. If she starts to tip to the side while sitting up, she bounces against the inflatable side of the tub and doesn't bonk her head on hard surfaces.
The bottom of the inside of the tub has little ridges to keep baby from sliding around. The bottom of the outside of the tub has a suction cup for hanging the tub to dry after use. As a bonus, the duck quacks when its bill is squeezed--great for distracting a baby who keeps trying to grab the shampoo bottle.