I presume paying the fee only applies if you must reserve seats ahead of the check in opening? In other words, if you don't pay, you log in 23hrs and 59mins before flight time and select your seats then when you check in?
I'd just do that tbh. I don't think I have ever experienced a flight where the majority of seats weren't available at check in and you could just pick them.
I have always thought that paying extra is for those people who must have the emergency exit row. At 5ft 9 and a veteran of a few hundred crappy, cramped long flights on dubious 3rd world/former Soviet Union airlines into and out of various oilfields I don't have the requirement