I rode the BRP last year with my wife for a hundred miles or so, then took 421 back North and spent the night in Bristol.
While I had a ton of warning about LEO presence, I didn’t see any during my time on it. And yes, the speed limit is low. But I stayed at comfortable speeds of 10-15 over, and got lucky to not have haf any trouble. I’ll tell you though, that pavement and those curves just beg you to take them faster.
Its a beautiful road. And mid-week, traffic wasn’t bad. But just the threat of a ticket kind of tempered my enthusiasm. Still worth the ride though.