I agree with what Daniel said about jumping the gun and challenging design assumptions (though I disagree with some of the other things).
I've used ngMaterial on some of the products I've managed where it was a good fit, but have worked on plenty of others where Material Design was a poor fit. You want to be thinking in terms of iteration and customer development.
That said, here are some important distinctions between ngMaterial and Bootstrap. ngMaterial relies on Flexbox, which doesn't have the best browser support. If your customers include corporate, education, or middle-aged Americans, that's bad news. Material Design is also very familiar to Android users (and can work well in generic web environments with younger demos where playfulness and interactivity are important), but Bootstrap feels much more "normal" to most users.
On one product, we discovered that our customers were not as youthful as we had anticipated. Material Design was a poor fit because, to exaggerate just a little, it didn't feel like Windows XP.
Anyway, the moral of the story is that there are no facts inside the building. If you're in an early-stage startup, talk to customers, validate the problem, validate the solution, and get quickly to an MVP you put in front of them so you can test. But make sure long-term design decisions are delayed until you have more facts.