"Bulletproof Coffee" the coffee brand is really light, not much flavour. I wouldn't buy this for myself or really recommend it. But I got it as a gift and well, I can't say much about it.
"Bulletproof Coffee" is also a name for putting butter in coffee.
And, as much as I would like to say otherwise it can be good.
Butter in coffee is the same as adding quite a bit of cream. And cream covers the taste of coffee.
If you normally drink it black, buttered coffee will taste bad, the coffee is muted and lacks the flavour that you are trying to achieve. I like some cream in mine so the butter thing, as long as it is unsalted is rather nice. If you use crappy butter it will be gross no matter how good your coffee is. Use grass fed butter. I use KerryGold.
If you like coffee with lots of cream, then it is good. But I would not use coffee that tastes good. For me, I find bulletproof coffee reminds me of a cappuccino which I love to have as my breakfast. The rest of my day, I stick to my french press coffee.