I highly recommend getting it if you are interested in acquiring multiple old guns, if you can be around to sign for packages. The amount you save on transfer fees alone is worth it. It also simplifies in-person purchases too, especially out of state.
The guns in question must be either 50+ years old, on that ATF list, or must derive a majority of their value from their historical connections (like, say, a gun owned by a famous person). It’s not just SP1s, there are thousands and thousands of guns made before 1972 that are all available to you as easy as buying, say, ammo online.
I have not found it terribly helpful with acquiring ammo, mags, or discounts but that’s alright, anyone with an LTC can get those things pretty easily anyway.
Many dealers don’t want to deal with C&R, or they don’t want to deal with Massachusetts. But there are enough who will that it is a nice thing to have.
The license is easy to get and relatively fast. If you can pass NICS you will get it. In terms of privacy: the ATF can knock on your door and ask to do an inspection but you can request that it be done some other time at their office. In 2020 the ATF inspected 3 of the 54,000 C&R licensees in America. Three. And you do have to retain records of all acquisitions/dispositions of qualifying guns but if you let your license expire every three years you are not required to keep the records. You do have to notify your CLEO that you are applying, but just send it to whoever issued your LTC, they already know you have guns. One of the few benefits of the MA LTC system: you already have no privacy in gun ownership from law enforcement
There are some minor benefits as well: no worries about the roster for old guns, being able to ship any of your own guns back to your house while traveling (FedEx/UPS want to see an FFL), being able to demonstrate that you are not a prohibited person if anyone asks, slightly easier Garand ordering from the CMP, it is a stepping stone to a MA machine gun license, and generally a better understanding of the firearms industry/ATF through personal experience.
Oh and I forgot, if you’re out of state and you see an old gun at a yard sale you can actually buy it! Been waiting for this to happen to me!