Too Much Info

I'm very new at this spa search process. This board has been a wondeful help. I'm looking a a Viking 2/3 person spa. They say that their contruction is of high density polyetheline, with a lifetime warranty on the spa shell. Aren't most spas mad of acrylic? Hot Springs told me a one year warranty on parts and labor. That seems to be quite a difference. Also because they are manufactured in MI, they are supposed to be designed for colder climates and would contain the heat better. Could this be true? Is a 4 HP motor big enuf for a 170 gallon spa? Thanks for your feedback.