Yep - they're weird alright .... but effective: the air line is on a swivel and the 'butterfly' refers to the wing shaped trigger plate that covers the entire top of the tool.
By squeezing either left or right on the plate, the gun direction instantly changes. It is very easy to control force and speed ... and they slip into more tight spots than pistol grip deals, as they nicely fit into the palm.

Definitely weird ... so I save it for use on my car: for others, I pull out the BFH and an impact driver