After two years of purchase and a thousand unresolved problems, I'm giving my assessment.
Aesthetically, the gearbox is very nice. Unfortunately, the positive aspects end there. The mechanism creates a lot of friction, even when no gears are engaged; it slides really poorly, and it also makes unpleasant mechanical noises. It can't be lubricated, because if you do, the clutches slip. I managed to use the model with this gearbox, but only for a few hours—very few. Then the clutches wore out, and no replacements are provided!
Disassembly and reassembly with the right spacing isn't exactly easy, and some pinion retaining screws are stuck with strong threadlock. I'll conclude with a personal observation: if they'd designed a gearbox coupled to the engine via a centrifugal clutch, it would have been much more enjoyable on models like my hotrod; furthermore, the clutches wouldn't have worn out so quickly.