I used Aptasia-X for a while, but I had to keep using it and it did nothing to stop or even slow down their spreading around my tank. It actually seemed that they spread faster after a while. Then I picked up some Berghia Nudibranchs and thought they were doing nothing at all. I couldn't see them at night and my aptasia was getting out of control. I only picked up 5 (3/4") ones for my tank (34 Gal DT) and thought I didn't get enough..........which is probably right. After about a month though, I saw my aptasia "garden" shrinking fast. A week or so later, and I only see 1 or 2 on the overflow.........visible parts of the rock work are clean (and I'm seeing the little critters all over the place now.....even in the sump).
So with all that being said, I'm a big proponent of Berghias............. :)