The products I owned were "residential" grade but a former co-worker bought one of their "almost commercial" grade ZTRs and that too was junk. The frame on the 33" walk-behind I bought cracked, same thing happened to former co-workers ZTR. The 33" walk-behind was purchased at an independent dealer, not a big box store so luckily they worked with Cub and got about 90% of my money back. I then purchased a used Scag walk behind which was well worth it.
I now live on 5.5 acres and mow probably 2.5 of that. First year I mowed with a Kubota BX2200 and it took two of us about 4 hours (me on Kubota, her on her Cub lawn tractor). Not only did it take forever, I felt like I just rode a bull for hours when I was done. So I went out and bought a Ferris ISX2200. Night and day difference. Mow faster and MUCH more comfortable due to the suspension. 2.5 acres doesn't seem like much, but I would not want a homeowner grade ZTR, it would get destroyed in a couple years. If you can, increase your budget and get full commercial, or like others have said buy a lightly used commercial grade. I have a pretty steep hill that I wont use the Ferris on, so I still have my Scag walk behind. I think it's probably 20-25 years old. Great mower!