The issue is -- how regularly will release 2 F upgrade seats at the same time, on the route you want. Versus one seat at a time, which frustratingly gets allocated to the next person on the list who is not a group of 2....
It’s pretty common, in my experience, for multiple U to open at once when U opens at all, but no guarantees that there will be any U at all before the 75K window opens, and then it’s too late (unless the upgrade processor screws up, but that’s a different topic).