We recently purchased a used model 140 (two person) spa on Craigslist for $300, or about 1/10th the purchase price. It was hardly used, although dirty and required a good cleaning.
We bought this for a vacation home, and it works well. We have a traditional "hot tub" up North, and it requires winterizing and storage, and critters are always trying to live in it (don't ask). Large tubs also need 200V wiring, which doesn't sound too bad, but I spend nearly $300 in copper, connectors, service interrupt, and conduit to connect the tub up myself (and electrician quoted nearly $2000).
So the 110V connection on the softub is a big money saver.
It pays to download the users manual from their website and READ IT COMPLETELY Over-chemicaling is the biggest no-no with a vinyl liner pool and doubly so with this tub. You will destroy the pump and the liner with too much chlorine. The tub does not need a lot.
The design is rather ingenious, as it uses the heat from the pump motor to heat the tub. This saves energy (my regular tub vents out this as waste heat) but it also means the tub will be slow to heat initially. It also means that it probably won't maintain temperature in severely cold weather (subzero) like our full-sized hard tub will (it is nice to go out on a snowy day and sit in a hot tub, too!).
It also has an interesting built-in automatic programming cycle that requires nothing more from you than to select a temperature. It has a built-in ozone generator as well, that is controlled automatically. It really is no-hassle from that perspective.
My neighbor has a softub as well (4 person) and they enjoy it in the summer. After nearly a decade, they report it is not heating as well. I am not sure why.
I do know that in a decade's time, our "regular" hard sided hot tub went through three covers, two pumps, and two heaters. These are not cheap items to replace, either - the pump alone cost more than we paid for this softub.
It is easy to move and can be rolled inside for storage off-season. We moved ours home strapped to the roof of our SUV (read the INSTRUCTIONS for tips on moving and strapping!).
So, my recommendation: If you can find one used (lightly) you will save a lot of dough. For what it IS, it works well. Trying to make it into something it ISN'T will cause problems. Look at the sizes listed. Like camping tents, the capacities are often optimistic (the two seater is nice for 1 and cozy for two, etc.). It is not a bad product, but it is not a big hard-sided 220V Hot tub, and if you try to use it as an alternative to that, you will be disappointed.