I'm not a dealer or know much about the different spa companies, but for the money you're looking at you should be able to get the same 'deal' on a 'name brand' tub. i may be wrong but don't think so.
You're on the right track, wet test to see if you get the therapeutic results you want. Test more than one company, too. Normally, stairs, delivery/set up, starter chems are throw ins. I can't imagine you getting a choice of stairs or stereo system, if you have 'skill one' you can make a set of stairs, take the stereo. How about a cover?
You may not get much of a response over the weekend from those who are much more industry savvy than me so don't get discouraged.
Happy testing