I just bought my second used commercial walk behind for my 1 acre lot. The first one lasted seven years (a Toro 44"). My latest is an Exmark 48" Turf Tracer HP.
Why commercial? First, I can't easily use a tractor or riding mower on my property because of all the trees. Therefore, my choices are a consumer mower, commercial walk-behind, or some sort of ZTR. For me a big factor is my time. It would take me more than twice as long to cut my lawn with a 21" mower. A second factor is appearance. I think it looks better with the cut I get from a commercial mower.