For me, the free middle seat has perfectly worked domestically. However, I would say, in case of morning OUL flights, they just closed the first 5-10 rows at some point, so it has never reached the point when those middle seat get occupied.
On other routes, I can tell I often see empty seats everywhere around the plane, but the one next to me is of course taken. It is not like that everyone could pick the seat, but I think staff allocates those and overrules the somewhat automated system of not offering the seat next to you to a lower tier passenger.