I don't know why they would be considered as DR kit. As far as I think, they are a small mobile tool box for a fitter/mechanic. I don't recall ever seeing one attached to a bike?
Do you mean these, I have wondered about them for years, I suspect they are just a small tool box for a fitter or artificer to carry minimal tools for small specific jobs, the motor cycle misconception comes from their resemblance to early bike tool boxs, but I'm ready to learn differently.