If it was really a steal then stick to your guns and get them to fix it. I don't know a lot about zero turns but know some folks who've had good luck with Ex-Marks.:Welcome1: :goodl:
I agree with shadow1961, in that you should give them a week to fix it for good or take it back. Sometimes a deal too good to be true really is.
As far as the rest of the mowers on your list, the reviews seem to be consistent with box store purchased mowers in that price range. It's awesome to it's the biggest piece of junk on earth. Looks like you limited your shopping to Sears, TSC and HD. There are more machines out there and some are at real dealerships with real service departments.
Go get a Z225 at the JD dealer so you will at least have a dealership with qualified people working on it. Not claiming it's any better, but you will have service.