2what it changes
Every friendly bee you produce gets a coin flip to come out as a Giant Bee instead, and the big ones are simply better at the same job. It applies across the board: the bee weapons, the honey accessories that spit bees out when you take a hit, and even the swarm released by smashing a Hive. A couple of sources also get an extra chance to fire a second bee on top of that. The accessory quietly helps two other things as well, speeding up Hornet Staff minions and adding damage and armor penetration to the Wasp Gun.
where it backfires
More bees is not always more damage. Friendly bees trigger global invincibility frames, so any weapon whose own hits are competing with the swarm can end up doing less overall. The Bee Keeper and Hive-Five are the two that suffer, since their own bees eat the frames their main attack needed. The Bee Gun and the Honey Comb line have no such conflict and take clean value from it.
when to wear it
It comes out of an Expert Queen Bee bag, early enough to carry a summoner or a mage through most of pre-Hardmode. Bees pop the moment they touch water or lava whatever size they are, so it is dead weight in an ocean or the Underworld.