Predominately, companies that buy a shell and build their own spas usually do a very poor job. They don't have the benefit of educated engineers, take short cuts, use cheaper components, etc. NO VALUE for the money your are spending. Also, I usually see them prorate their warranties and have heavy fine print protecting them, not you.
Buy from a reputable manufacturer and save in thelong run. there are a few compnaies that rated spas to help you determine who is doing a better job-consumers Digest and Spa Search