What is the battery health of your 3?! I upgraded from a 4 that needed to be charged twice a day after battery dipped below 80, which made it not very useful for me.
So now I have it as a backup and it gets turned on like once a week when I need a watch but my 7 is charging! (If you go this route, make sure to charge old watch to at least 60% and then turn OFF from the settings menu til you need it next time).
Is that price for the new S9 for a stainless or titanium case? U1 has been on discount (in the US anyway) basically since the U2 was released, so if the used U1 is priced similarly to an aluminum S9 new, in terms of value for cost, the used U1 seems the way to go. Otherwise if you’re looking at a new stainless steel S9, I would think you’d be able to find a new U1 for a better price than that used one. (Disclaimer - I did no money conversion, so that could be confusing me)