As far as the case: I’ve only owned the stainless steel and I’m a runner. I’m sure the aluminum is lighter but I don’t find the SS heavy by any stretch!
Bands: I prefer the Sport loop for running, golf, etc...as you can adjust it very precisely to just the right fit...so it’s not slipping around your wrist!
If you have big wrists, beware of the sport loop! They’ve taken some length off it in the past couple of years! I just bought the 5 SS with Alaska blue sport loop band....and I’m gonna have to return the band and swap it out for a regular sport band...as it’s too short! The end of the band sits on the side of my wrist (not at the bottom) when it’s on! Looks weird! My wrist is 8” (the Volt yellow one just barely made it to the underside of my wrist when strapped on). See pic comparing the yellow sport loop band I bought a couple of years ago with the new one!
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