I'm trying to compare different Swim Spas and use in the winter in Northern New England. Is there one that is better insulated or has a better cover? Is a dual heater system better for winter use or does it not matter? I want a spa that is therapeutic, but allows for a good work out for both myself with bad knees and my 6'3" athletic husband that we can enjoy in the summer but use through the winter months 3-4 times a week.

Thanks for any ideas.