I just want to say that the Magic Mouse is the best mouse I've ever used. Having a touch sensitive surface is huge, and that's why it's not curved too much. I've been using it since it came out and I've never had any issues with ergonomics. You just need to make sure your chair is at the right height and you have good posture, you hand goes over it mostly flat which is closer to a resting position. Trying holding the mouse between your thumb and ring/pinky fingers, with your pointer and middle resting lightly on the surface. This has always worked brilliantly for me, and I have lots of different gestures configured using Better Touch Tool. It helps me get my work done quickly, and the scrolling is so much smoother than a wheel, like a trackpad.
Of course the charging port on the bottom sucks, but when it happens while working, I can just flip it over and plug it in and go take 5 to go to the bathroom, get some water, or take a clarity break to get some fresh air outside. By the time I return, it has a few hours of charge, which is usually enough to get me to lunch or the end of my day, when I can leave it plugged in. I'd love for them to put the charging port on the front, especially since it would rest between the fingers and not cause any issues, but I doubt they ever will. They'll probably just get to the point where the battery in a future version lasts so long, and the quick charging via USB-C is so fast (a minute or two to get a day's worth), that fewer people will complain.
As a designer, I see it as a challenge. They could probably engineer some mechanism to pop the front top shell up a few mm, just big enough for a USB-C port, that would stay cocked open slightly while charging.
