The O-72 restriction is due to the close coupling and the wheelbase of the powered unit -- it would require too much swivel on anything less than O-72.
I have two of them and both have had one issue or another (cracked gears; wires too thin to add more than one car). Since they're out of warranty, I'm going to crack into them and fix them so they'll run properly in a prototypcal for Amtrak 5-unit consist). The sound and engine lighting are spot-on and it does look impressive running.
I'd recommend against getting one off eBay unless you're sure of its condition and I'd recommend running it in the as-shipped 3-unit consist. The VIA train ran a much longer consist (9-unit as I recall) which won't work with the MTH model as-configured due to the thin interface wires.
