One negative, think I'm a lousier lane changer with the Prius. To be fair, with every new vehicle we get it seems rear and rear-corner visibility degrades, but the Prius hits a new low: I do NOT trust what I see (or miss) when shoulder-checking. The high waist waist line, split rear window, thick rear pillar, head rests: all work in concert to confound my peripheral vision. I've learned to be really cautious with lane changes.
Safer with more tolerance for sure: 1. Can't pass anyone so might as well stick behind a truck until you see the exit. 2. People pass you left and right for some reason (I drive at normal speed as driving non-hybrid) because of the Prius. You'll used to it and don't care anymore.
Does driving a Prius make you a better driver? Personally no...but I still save a lot of money on gas. Third party "you", that's debatable.