You got that right! Besides not being engineered for pulling, "zero-turns" suck on hills (they're dangerous). We run two John Deere 445's (tractors) with hydraulic lift pull-behinds which weigh well over 500 pounds. They're great in wide open areas and handle slopes fairly well (much safer than zero-turns). Total cost per tractor & pull-behind = BIG MONEY.
I've been in this business 30 years now (started with ChemLawn in 1978), and if I started from "square one", I would utilize TurnAer units with sulkies on my big open areas, then use their smaller units to do the trimming.
2nd choice would be Ryan, as they stand up well too.
Keep in mind, we have had decent luck with Ryan units, but it seems that Turfco offers the same quality or better.
Customer support? Turfco >>>>> bar none.
That my honest two cents. Hope it helps. Larry.