I'm no pro, but I have the Z2 as well. Can't really compare the 2 you're looking at, but I am very happy with this machine. I"m coming for a Hustler RaptorSD, so it's quite a bit more machine and it's noticeable. Took me a cut or 2 to get used to it, but things I like about it.
Cuts well, plenty of power, i like the safety switch that I can just hop off and pick something up and the blades shut off, get on, quick half pull of PTO and i'm off and running again. I love standing over sitting, but like I said, it took me 2-3 hours on it to get used to riding with the machine and not trying to control it by being rigid. Rides very very well now, I cut twice as much as i did with my old mower in about the same time and with half the stress on my low back. superior on hills compared to that too. I imagine the Z1 has the same sort of benefits.
I can't really comment on scag, and like I said, i'm just a homeowner.