Its not that res MP's don't do much. Its that we do not have the same mandate as the reg force MP's.
In the land component, reserve MP's train and do all the same things as the reg force ones, aside from the law enforcement part.
Last year, I spent 135 days in uniform, on training and taskings.(no long term class B). Right now I am in Cold Lake, augmenting base security for Maple Flag 38. Anyone telling you that res MP's do not do much are way off mark.
However, if you join the reserve MP's and spend only 6 months with them, I will advise on avoiding going throught the trouble. If you have 4-5 years to commit to a reserve MP unit, chances are you will get a lot out of it that can help you in your reg MP career. But for such a short time period the mountain of paperwork and red tape will not be worth it.
Also, you can not directly transfer from a res MP unit to a reg MP unit. You would have to go throught all the steps any one from off the streets would, or close to it.