There are other masks that are just as efficient. But wearing eyeglasses creates a whole new problem, keeping the glasses from fogging up. The RZ has an adjustable nose piece to create a seal at the top and one-way discharge valves on the front to allow condensation to escape which prevents fogging. It really works!
But alas I had another problem, a beard. It is impossible to create a tight seal with any mask when the user has facial hair. But the wrap around design allows a good seal, better than others I have tried.
The M1 is designed for use in cooler weather, so it can get warm using it in the spring and summer. They offer the M2, a breathable mesh for warmer weather. I will be ordering the mesh M2 mask soon. If you're looking for a good dust mask, give this one a try.