Hello Thursdayschild,
I endorse RogerL's comments, but there are limited circumstances where either the CamperTrolly or Steve's ET mover (Or any other Aframe based mover) can work very effectively.
In essence if the mover is only ever going to be used ona near flat hard surface (Such as a factory or yard) then they can be a simple and very effective aid to marshalling caravans or other trailers.
For the reasons Roger explained and indeed Steve described, All A frame movers suffer from limited grip, Its not so much the power, but the ability to use the power. Strangely its not the ability of thge mover to actually move a trailer, but more importantly its ability to stop it on any sort of incline. If the wheel skids, then the caravan is out of control and a tonne of mass can do a lot of damage to both people and property.
As a guide, if you dont think you could stop a caravan from moving by your self on a slope, then it is quite probable that an A frame mover also could not stop a moving caravan.
Dont also forget that slpes can become extra slippy in the wet, or with dead leaves ,gravel, and of course ice.
Every type of mover has its limitations, but given teh same advers conditions A frame movers will let go far sooner than main axle movers.