"Have any of you used a horn when calling for moose? Any recommendations, or is a horn really beneficial? Thanks for the replies so far!"
On my Montana Moose hunt, I used a whiffle ball bat with both ends cut off as a "horn". It was one of the fat, plastic bats. I left the neoprene like grip on it to deaden the vibration a bit, and wrapped it in camo tape since the whole thing was neon green- it is a toy after all- a couple holes in the large end with a loop of 550 cord run through it allowed me to clip the fat end to my pack with a carabiner, while the skinny end either got strapped to the pack or placed in the water bottle pocket on the pack. This kept it from swinging around wildly. It definitely projects your calling better than hands alone, and it's a much cheaper alternative that an advertised "moose call". I've since repurposed it as an elk bugle for use with a diaphragm, and it works great in that capacity as well. I would also recommend a beef scapula for raking trees. I found this to be far more effective for drawing in bulls than any amount of calling.