Pearl, due to the fact that I'm losing all my fencelines here and completely not where I want to be with trail development for personal/animal exercise, I've been looking into mechanized brush cutting options. Of course I utterly cannot afford the multiple thousands for a heavy duty walk-behind brush cutter, and in fact it would be cheaper to buy an ancient used tractor with brushhog attachment. (I will probably do this, but the guy I rely on to help me with tricky mechanical rehabilitations is elsewhere for the indefinite pandemic-deranged future, so it's not a this-year ambition.)
While wistfully window-shopping online for brush cutters I can't afford, I stumbled over the "unwieldy" walk-behind string trimmers like the one in your OP. I have one on order because I think I can wrestle it around with reasonable dispatch and it was within my budget.
However, my reason for posting is that while shopping for my walk-behind string trimmer, I discovered that there's a sort of hybrid category between hand-held kind and the kind with two wheels and a heavy steel deck that you posted and I am buying. It's also a bit cheaper than the heavy-steel-deck kind. It sorta looks like a short handheld string trimmer mounted on two wheels:
I don't know if that's enough lighter and easier to control to interest you, but I thought I'd post it here just in case, and anyway it might solve somebody else's problem.
I was also amused to discover this 80-year-old man who took the cutter-bar type electric hedge trimmer and mounted it parallel to the ground on a frame made with steel tubing and bicycle wheels. He did it to solve a very specfic problem (a dangerous-to-him ivy-covered slope) but it may suggest innovative solutions to other problems:
I'm going to see how I like my heavy walk-behind string trimmer with string, before worrying about modifications, but I am very interested in some of the alternative cutting heads that people use on the handheld string trimmers. However, I don't think I'm crazy enough to just mount a lawnmower blade on it (spinning out there without any housing around it to protect the user from flying rocks or broken blade fragments) like this kamikaze gentleman on youtube: