is mouse sensitivity important in bullet games?

I think you should just use whatever you always use since that's what your most comfortable with!

Seemingly a sound line of reasoning, until you consider the entire discussion of DPI ranges also adjusts for how much physical distance the mouse needs to move to register cursor input, although that could be something to consider if perhaps your peripheral vision is not the best. I always like my gameboard to be as large as possible, but that's just my personal preference.

It just depends on ur own preference, its really not specific.

If u have a small pad for ur mouse, with little room to move ur arm, higher sensitivity is more useful, and vice versa. 

but really it just comes down to what feels natural for ur arm and eyes. 

Best in my experience is an iPad mini or similar. You can hold it in one hand and it's big enough to see but still super fast to move.