The unit is held in place by a butterfly device that is expanded by the center bolt.
Benny is right, it uses an external power source & in this case it will need 110 volts which should not be too hard to achieve.

From past experience with a similar unit, what happens is that the coolant is progressively warmed untill the thermostat begins to open. At this point the coolant begins to circulate into the radiator via thermo siphon, so all of the coolant, including the radiator will have 'some' heat.

The temperature should not get to normal operating temperature, probably about half way there, but in a closed garage, given time, the whole block, & all internal parts will be well warmed, including the oil.
Once started, the engine will reach full operating temp much more quickly, keeping in mind that the block casting itself will be holding heat, & the heater will produce it's foot warming flow immediately.

As to taking the car out & flogging it immediately? Surely nobody would do such things anyway as the trans & diff oil are still cold & thick, so will need to be run for a time before any decent rotational speeds are achieved to prevent needless wear in these units.

It's not for everybody, but I like it, & that's all that matters.