The JM Pro is finished slightly better. Things like the loading gate/elevator, charging handle, are all "upgrades." I'm not sure but I thought I remembered one of them couldn't take chokes, but that was a while ago, so don't take my word for it.
JM Pro upgrades-
•Chromed gas piston assembly, hammer, sear, and mag tube
•Nordic Comp mag tube extension
•Beveled loading gate and shorter forend
•Extended elevator
•Oversized charging handle and bolt release
•Trigger over-travel stop