I am also debating between the cbr125 and the ninja 300.
My mind was set on the ninja 300 before the training course. But after the course, I am not too sure.
Because I still don't feel like street-ready after the course, so I am starting to think maybe it is not a good idea to get a 300 when I still haven't master the 125...
I felt the same way after completing my course. I still bought a ninja 250 the next day but just practiced in mh neighbourhood and at an empty go transit parking lot on weekends. I just kept practicing every day like this until I felt comfortable
Get the bike your heart wants.