Opinions on that vary, and that's ok. We did a lot of research before getting one (and were willing to go the $400 for the bench model) and the opinions were split exactly 50-50. Even our orthopedic surgeon prefers (and has) a door unit.

I don't understand what you mean by "15# just to unweight your head"; would you mind elucidating? I've never even used the water bag; I didn't trust it not to leak, and it seemed too.... imprecise, so I just tied a hook onto the cord and hang known free weights.

Doc