Bought this gizmo at BBB.
Ok, when you press down hard on the center part into the drain, the outer lip DOES make a good seal against the tub. And the center part gets somewhat of a seal against the inside of the drain. Must be made of a particular kind of plastic conducive to that. That's good news.
Some of the hair gets caught up by the outer ring, which has a bunch of little "thorns" sticking up to catch it.
But the long slits around the sides of the inside of the center part are poor design. When hair piles up in the center of the bottom of the gizmo - - blocking the holes there - - water (and hair) will then try to flow out through the slits.
The section with the slits is only partially sealed against the side of the drain. Not enough to stop all flow of water & hair, but too much of a seal to let water flow freely, so the shower starts backing up in water. And yet the hair is getting through the slits.
When I took the gizmo out there was a ring of hair around the outside where the slits are. Proof that hair was flowing through the slits and that some hair is going on down into the drain.
It's a pain to clean. You have to pick out what hair is wrapped around the 'thorns' and you have to clean out the center part ... and then clean off the hair from around the outside of the slits. I had to clean it completely after every two uses ... or water started backing up immediately.
It's obviously doing somewhat of a good job, but I am still going to have a clog problem eventually since hair is getting through. And in the meantime, I have to constantly spend time cleaning up the gizmo.
Right now I am awaiting the arrival from Amazon of
Danco 88821 2-3/4-Inch Tub Mesh Strainer, Stainless which I hope will be more effective and easier to clean.
[UPDATE: July 29, 2009] I got this thing to get a good seal against the sides of the drain, so that the water (with the hair) can't flow out the long slits. Not surprisingly, water backs up in the tub once the few, small holes at bottom are covered with hair & soap scum. So far, the stainless steel version mentioned above appears to be working much better.