The advantage of Soft tubs are as follows:
Portability
That's it!
They are a glorified kiddies pool with no therapy, no comfort (sitting on the floor) and no heat retention (115V). Often they can cost $2000+ which I find criminal and that money could be better spent on a used spa if cost was the factor.
If it's a soft sided "spa" someone wants, go to your local ToysRus and buy an inflatable wading pool and then stop on your way home at Costco and buy a case of baked beans. You'll get similar results!