Fuel filler hole is much too small.
Kickstart lever hits the footpeg.
Diaphragm clutch requires a lot of maintenance.
Must remove engine to remove cylinder.
Must remove engine to access fuel pump.
Gearbox is potentially weak and very difficult to rebuild. Using aluminum for the shift drum was really shortsighted.
ECU is in a bad spot: early (inside airbox) late (above head).
Using small non-magnetic fasteners. Okay, they do not rust but you can not retrieve them with a magnetic pickup tool.
In general, too little attention was paid to ease of maintenance.
There was no mechanism to communicate with early adopters about what would improve their bikes as OSSA improved the later models.