I've had my C&R license for almost a quarter century. Never regretted it. It is worth its weight in gold if you like old guns.
mOpar's point #3 in his post sums up the biggest problem you will face. Sometimes, the dealers who do recognize it will still insist you fill out a 4473, which isn't necessary, but you can't talk them out of it! Then there are the ones who insist that a gun has to be on the list to be a C&R. NO! The list is a list of exceptions to the fifty year rule.
By the way, machine guns ARE included as curio and relics. Of course all NFA rules must be followed when transferring them.
I have found that most of the big stores (Cabela's, Gander Mountain and Bass Pro Shops,) recognize the license. I was travelling from Illinois to California one year and spotted a beautiful 1891 Argentine Mauser in the Cabela's store in Sidney, Nebraska. I signed a copy of my C&R, paid for the gun, and walked out with it, right then and there, no 4473, no background check. Whole thing took ten minutes.
Ya gotta love it.