Yes, and most carriers offers first 3 months free for the watch plan, so no risk here!
Not sure how that would work if you signed up for LTE service, but canceled to return your watch. May depend on your carrier.
I didn’t sign up with ATT until I had my LTE watch for a few days. During signup, it said I would get credited for the one-time activation and 3 months free sometime within the first 3 bill cycles. Not sure what happens if you cancel.
Indeed my first bill shows no credits and has the $25 and $10/mo charge.
So I guess worst case is you might have to pay $35 to try it out on ATT.