I have some thoughts.
I have a Xiaomi phone, and a Xiaomi Mi band. Great hardware at good prices. I do not have the Xiaomi software for either. That is increasingly difficult (certainly on the mi band front).
The mi band...for £20 does the three on Russ's initial list. I use it through gadgetbridge. One of my essential criteria for putting something on my arm and carrying it around with me is: "is supported by gadgetbridge". I will not pay a lot of money to carry around a data collection device for data connected organisations to conspire to put up my hotel room, taxi rides, and meal prices. "Smart watches" are also really wank to use. I carry a phone, unless I am under water, so I don't need something that works worse. The advantage of a sports type band is that it is easier to wear, in a wider range of circumstances, and is something I don't mind wearing all the time and putting into jeopardy. Because it's fucking cheap (and waterproof, and small and not subject to being easily scratched or banged - especially worn inside or outside the wrist to suit the activity. Can also be mounted on a highly stylish surfer dude type string around the neck.). Under no fucking circumstances am I having a payment mechanism on an expensive watch. I can see too many obvious modes of failure.
Have you considered getting a compact cheap waterproof sports band, and when you are going somewhere nice pushing it up your arm, and wearing a dress watch of your preference? You wont look like a knob, and the battery wont wear out, or the software become obsolete.
Xiaomi probably sell more devices than any of the brands that you have heard about. I cannot think of many manufacturers who are not hell bent on reaming you out as much as possible, at your expense. I would be more than nervous about putting a payment mechanism on any watch (or ring, or butt plug). I just wouldn't do it. As we have discussed before I find bank cards perfectly functional.