I don't have it, but I've read about it. For it to be worth it depends on some variables. First when coming back to the U.S. on an international flight, it will get you through Passport control quicker. Apparently you just go to a kiosk, the machine scans your fingerprints and passport and bingo you're in the country.
BUT.....you've not collected your bags yet and thus have not cleared customs. If you've hunted on a farm which is what most RSA operations are considered, you'll have checked that on the Customs form handed out towards the end of the flight. Also since you're traveling with rifles, you're virtually guaranteed to have a moment with a CBP officer to verify 4457's against the rifle serial numbers. Now from what I understand if you show them you have Global Entry, they'll move you to the front of the line.
Also, what if you're bags are the last off the plane? The time you save breezing through Passport control may just get chewed up at the carousel. Of course you'll have your place at the rail, and personally I always try to be right where the bags come out to prevent my bags from walking away. My mother-in-law had some clown at DFW try to take her bag, not sure if it was a mistake or not, but either way had she not seen it, it was gone.
In the end I'm not sure it's worth it or not. On my recent flight from Germany there were actually very few Americans on board as evidenced at the short line at Passport control. Clearly there I would have saved no more than a minute or two. And again, I had to wait awhile for my one normal bag at the carousel and a bit longer for the gun/ammo cases to come through the "special" baggage area.
At LAX they seemed to have a for U.S. citizens line and again it was relatively short. And again because I had guns, I got my meeting with the CBP officer to open up the case. I don't think in the end that Global Entry would have saved me much time on this trip and it wouldn't be worth the cost.
But change the circumstances with travel later in the summer and having many more U.S. citizens on board and it may have been a different story.