I know some people hate the idea but it's never bothered me -- what is butter, if not cream that's gotten itself all worked up?
I've had it a few times from relatives who swore by it at the time (fad thing, didn't last for them). It was okay -- interesting mouthfeel, and I can see how some people would like it. At the time, they insisted on its health benefits but I'm convinced that's a meaningless distinction and the only reason to do it is for the taste/experience.
I do love the name. "Bulletproof coffee." Helluva fad name, I gotta give them credit.
I won't weigh in on its effects on brewing, but I can definitely sympathize with the fear of a shatter-worthy temperature fluctuation. Ever since I broke a plate microwaving a frozen donut as a kid, I've felt hyperaware of the temperature in every glass or ceramics container I use in the kitchen.
Listen, Peelee, I know it's our patriotic duty to dunk on tea (or, preferably, dunk tea in the harbor), but you gotta lay off the "hot leaf juice" schtick.
The Brits, I think we can handle -- it's the Dragon of the West I'm worried about.