Nanook
F-notso-NG-anymore
I have been reading up on it from what I can tell having it removes the limit of buying a regulated firearm every 30 days. I can't really see any other limits or requirements.
Also very critical is it voids out the bits in COMAR 4-203 about to and from the range/gun store/gunsmith/etc. Let's say you pick a buddy up to go to the range (or a MDS shoot across the state). He/She invites you in for dinner and their significant other insists on everybody watching a TV show afterwards...fast forward: it is now midnight and you get pulled over on the way home. Let's say you did something to give the officer probable cause to search your vehicle. There are no ranges around here (that I know of) open near midnight. A reasonable officer would understand the series of events that day - an uninformed/anti- could cause some excitement or at least several hours of delay.
The designated collector status allows you to transport any or all of your collection, pretty much anywhere and anytime you see fit. Hypothetically, if I am taking folks shooting and have several match grade ARs and several bullseye pistol boxes full of lots of paychecks in the vehicle (especially cased long guns in the bed of the truck), I will have insurance. My insurance is to have an unloaded pistol and several loaded 15 rounders inside a closed case on the front seat. I would also keep printed copies of the COMAR 4-203, sections pertaining to removal of restrictions for designated collectors, the MD AG's finding that a loaded magazine does not constitute a loaded weapon, and a copy of my designated collector letter from the MSP right beside my vehicle registration and proof of insurance. This paperwork is not required, but if you need to have a 'teaching moment' on the side of the road, it would sure come in handy.
YMMV. IANAL.