Agree the Roco F9 drives have some good qualities but the awful truck design is terrible, tending to shed the truck side-frame like a crispy scab. The NWSL wheel/axle/gear replacements mitigate some of the drive issues but (opinion) ultimately still a dead end, though at least spawning a good after market business in drive replacements. I'm weighing the efficacy of the "John Armstrong" modification to the truck frame as I sit on huge junk inventory of these.
The Rivarossi drives on their FM CPA-4-1500 model is a completely different issue, basically a truck mounted version of their HO drives, awful for any real operation but not bad if you just want to run around in a circle with a light delrin trucked consist. I like them if for no other reason than they sound really cool.
