I have a monster mill MM3 and it works perfectly. I got the one with the larger rollers thinking that would be more friendly for millet but there are lots of people that use various versions with success. The only critical thing is that you have to be able to adjust the gap. If I had to do it over I would have gotten the two roller version rather than the 3 roller. For millet, you set the gap with feeler gauge somewhere between 0.010" and 0.030" depending on the crush you want and run it through either once or twice and your fine.
Since my grain bill always has less than 20% buckwheat and rice, I just mix it in and run it through together with a gap of 0.020". It works just fine, but if you have large amounts of buckwheat or rice consider running them through separately with a larger gap.