Speaking from a law-enforcement perspective and past observations, yes, you would be in possession of a prohibited device, and would likely suffer confiscation of all your firearms-related paraphernalia and potential jail time. That's if you were a law-abiding citizen with a clean record. Now if you were a lifetime career criminal, and had used those prohibited devices in the commision of a crime, the police would do the same things to you and you would be charged with the same things, but you would most likely go free in a few hours with our sincerest apologies for taking time out of your busy schedule. Either way, you would never see those mags again, and it would probably be years before you got any of your other property back, if at all. True, you might be able to go to the range for decades without arousing any suspicion or coming into contact with any LEOs, but then you could get caught with those things tomorrow and have years of legal battles ahead. Nobody needs those hassles. Get your mags pinned. Cheapest insurance there is.
Erik.