It seems to be the most common item people buy (because it can actually slightly affect your performance as it better matches the hitbox, and it is the most used competitively). I know a lot of people who never bought a single item, except for the fennec.
The fennec hitbox is the same as the Octane, but the design of the car better matches the hitbox compared to the Octane. So you can be more precise with your touches.
I have bought some items, but only by trading free drops for keys/credits.