We were thinking about that; but we denied it due to a couple of reasons:
1. the rest of the styles are very engineer-specific, so it'd be inconsistent to make the item equippable to both classes (since all 3 types of D.R.O.N.E. Pals are styles for the same item) (e.g. toolbox drone would make no sense on spy whatsoever)
2. Other than the sapper, the rest of the item is still completely engineer-specific: If you look closely, it's even made to look like it's made out of teleporter and gunslinger parts.

could make sense as a spy item as well