The MZ 5424S has a stamped 12 gauge deck instead of a 10 guage fabricated deck, Kawisaki FR series engine rather than FX with the heavy duty filtration system, smallish tires, slowish ground speed and it doesn't look like it will be covered under warranty for commercial use. Also no roll-over protection system, smaller hydro pumps and lighter transmission. I'd look into the warranty and confirm that as that could be a deal breaker. The MZ 5225 has the Kohler Courge Pro V twin engine...not sure if those are any good but it has slightly thicker fabricated deck and larger hydro pumps and a 1 year commercial warranty, as does the M-ZT-52. The M-ZT-52 looks pretty close to being a full commercial machine but not sure about the Briggs Endurance series engine. The M-ZT has a rollover bar as well. The website has those machines being $400 and $1,200 more than the MZ5424S.
BTW, all I did was do a specification compare on the website. You can simply click what machines you want to compare and it shows their specs side-by-side. And again, I have no first hand knowledge of these mowers.