Hello Roy,
Welcome to the forum. Thermospa probably isn't that well regarded here, but that is mainly for the companies aggressive home marketing practices. To be truthful, that maybe old news. I have been around this forum about 10 years and I haven't been bothered by them in many years.
I've seen a few of the tubs themselves and I find them neither top of the line or junk. They use fairly common components, so if you have some skill or help you might find this a rewarding project. That said, there are others here more experienced in that type of endeavor.
A lot of their designs have 2 or 3 pumps and one pump has to run in order for the heat to circulate, so you theory may be correct.