I use it on my gnome battlesmith, while mounted on his defender. I basically just treat the defender like a mech. A Saddle of the Cavalier keeps them from ever being separated, and the defender has a humanoid shape which means it has no difficulty with things like ladders and stairs that otherwise make mount use impractical indoors. The build uses its bonus action for Magic Stones in a 3-servant TSAR, but a build really dedicated to the concept could get the Dual Wielder feat and wield two lances at once.

The same concept would work well on a Beastmaster ranger. In many ways this would work better, in fact.