I bought a Thule towbar mounted rack because my wife couldn't cope with the roof mounted bike carriers (estate car) but the towbar model is quite heavy (20kg IIRC) and needs a fair bit of tightening when putting it on. She couldn't cope with it either.
That said we took 6 bikes to Burgundy from Scotland, 2 on the roof and 4 on the towbar, with no problems.
Once you work out how the towbar racks work and how secure they are then you will be fine.