I’m not very familiar with the Caldera spas, but am familiar with the Hotspring and Sundance.
$5,300 for a Prodigy is a really great price. I have seen the Prodigy as high as $6,700 in the New Jersey/Pennsylvania/New York/Delaware area. I recommend my customers to go 110V as often as they can to save some money. In my opinion, you don’t lose much when you go 110V, and you can always upgrade it later to 220V. Obviously, opinions vary.
In regards to the Marin, it is another smaller spa. I consider it Sundance’s version of the Hotspring Sovereign so the price should be around the same price as the Sovereign (within $500 dollars).
I would not worry about the leaky spa issue with Sundance. That was at least 6 years ago. Also, not sure if you know this, if a Sundance spa leaks in the plumbing (not equipment) within 6 months of ownership you will get a new spa. Your dealer is required to send the spa back to Sundance for testing. This came about because of their leaky issue back in the late 1990’s.
You asked a question about foot jets and wrist jets making a better therapeutic experience. Only you can figure out if the foot and wrist jets make a better experience. That’s why everyone on this board recommends a wet-test.