Mac<thing>: e.g. Macbook, MacBook Pro, Mac Pro
i<thing>: iPod, iPhone, iPad, iSight
Apple <thing>: Apple watch, Apple pencil
I think the Apple one is the worst, because <thing> seems to be common non-trademarked words and has a weird marketing exec "let's get the branding out there!" strategy.
And now it kind of smells like they might be thinking about going to a "Smart <thing>" naming scheme.
It makes calling things kind of hard and schizophrenic, most people just default to i<thing> when they don't know what to call it. I hear iWatch at least once a week.