I use the regular Ergoplay, it does help with back stress, which is the reason I got it. As far as which model you might like or whether you will like it at all is subjective. The Tappert model would be way too tall for me, I am short and the regular model at it's lowest setting is just about right. It takes a little getting used to, but any change in playing position is going to take some work.
I tried the Neck up, but felt it was too flexible, I didn't feel secure with it. The Ergoplay sticks better to my french polished guitar, since gravity pushes on the suction cups, it can't come off while playing. The system itself is rigid and secure so I can move around well, I tend to move a bit when playing so being flexible in the torso feels right. When I go back and try a footstool I feel much more restricted, and of course the tension in my lower back and legs is very apparent in comparison.
Unless you are just poor, I would recommend trying it out at least. If you are tall then maybe the Tappert would work better but who knows until you try. I know many players who are each happy with a specific support for whatever reason. The Ergoplay just happened to work for me. I would have liked a little more height adjustment (lower), but am able to get comfortable enough just by where I place the support on the guitar.
Bottom line is that it is a quality product, but trying it out for a period of time is the only way to know. If you don't like it you can sell it to someone, but $40 isn't all the big an investment to most people.