Can I use mountain bike lights on the road or will they blind traffic?

The answer, like anything, is: yes, but there are compromises...I'll explain...

How do I choose which light is best for me?

Completely depends on your specific use case and type of riding, here's a guide to get started.

What do I do if the mount doesn't fit my helmet?

Why don't you include a strap mount for your helmet lights?

Why don't you include every mounting solution possible with every light?