You'll be impressed. I took a momentary diversion from O gauge 18 years ago. I have 1 S-Helper and 1 AM diesel. They are smooth runners. If S had more product offering, I would have made the switch.
I am making the switch too late I see, but better late than never. The quicker I can sell my O & HO, the faster I can buy the American Models engines, freight & passenger cars, track and switches. I saw some new MTH F7's that caught my eye, I might even try to get one of the legacy berkshires.