What are the CPL exams like ? Is it mainly interesting stuff ? I'm actually quite interested in navigation 'cos I do a lot of hill-walking with a GPS/compass etc.
Some of it is interesting. Much of it is fixed wing orientated facts and figures which you need for the exams, and will forget immediately afterwards. As an instructor on R22s, I've yet to find much use for my now forgotten knowledge of machmeters, jet streams, or which degree of freedom it is if one country overflies another country's airspace but doesn't land there.
On the other hand, I do now understand met a lot better, I have a reasonable idea how my instruments work, and a much better understanding of helicopter aerodynamics. It's just a pity that my overworked little brain can't selectively remember the useful stuff and forget the crap.
Hill walking nav is somewhat different, I'm afraid. However, the ability to read 1;50,000 OS maps will help when you come to the CPL flying...except I bet you never tried to follow one while flying at 70kts! As a walker since childhood, I still remember my instructor's face when he told me I'd probably never seen one before, and I said I'd been using OS maps for years and years.