These US healthcare systems are effectively scams. Yes in theory they can save you money, however in theory there is no difference between theory and practice, while in practice there is.
Of course it’s a scam. “We’ll keep your money for ourselves and never give it back if you don’t spend it this calendar year”? Get the fuck out of here! That’s not to mention the hurdles they make you jump through every time you actually use it, having to upload or mail receipts, fill out forms, etc…