I have several of the walk behind string trimmers and have been using them since 1996. I have wore out 9 so far. They are Craftsman this newest group. The push a whole lot easier that a lawn mower, they balance well on two big wheels and are a bunch easier to use then the sickle bar style of self propelled trimmers.
I have tried the sickle bar self propelled, they are good unless you have to go around things that are close together but for my use I have found them not to be the best solution. I have one of the DR string trimmers and it is way heavier than the Craftsman.
Walk behind bladed mower is a spark throwing piece of equipment and I will never try one of those again.
If you have 5 acres to mow, nothing is going to be easy but I really like these for the lagoon I have to mow, all the fence line, around structures, around cars, around trees and concrete. I can handle these pretty easy with my bad back. Maybe try renting some different equipment to see what works best for your situation.