yup got all that. the dolly seems to allow you to quickly roll on, rotate and roll off, without fixtuing the adapter, lifting her up, then relowering and taking hte fixture off. I dont 'know maybe its just me.
I think what you are referring to is a pair of dollies, curved for the tire to set in w/4 wheels on it. Wheels that rotate 360, for moving the device anywhere.
Once the bike is in these dollies, you can push it any direction you so desire.
I have seen what I'm referring to used to stack bikes into tight spots for storage, like up against the back wall of a single car garage.