The use of A Frames are legal in the UK, but not in Europe. Most cars that are being towed this way are in the very small bracket such as Smartcar and are usually less than 1000 kg. The braking systems are not 100% efficient, but are probably as good as the overrun system we have on caravans, if you want to be realistic. In Europe you need to use a braked trailer and again it is usually the Smartcar that is carried. The trailers are twin wheeled and come with all the necessary fittings.
Many people ask why bother towing a car and what is the advantage over a caravan? It depends on your type of touring. Many people feel a large motorhome gives them the space and payload they want, especially as they get older. It also allows them to use Aires in France and set up more easily on site. I know we have motormovers etc, but they add weight. Yes, we have all laughed at the mtorhome user trying to get up on to ramps to level the van, but manylarge motorhomes now have hydraulic jack systems and it is a push button operation. It is also stated that by towing a 2nd car they are doubling their costs. Not true as small micro cars have very low tax and insurance, in fact often less than insuring a caravan. Fuel consumption is excellent, certainly far better than any towing car/4x4. So over a total holiday whereyou spend 50% of the time sightseeing, you can save costs with teh microcar. The total train length is probably the same as a car and large van, so again little difference. Cost wise the motorhome seems expensive, but then again you need to look at your lifestyle. If you are retired and do not need a car for work, then the motorhome can be an answer and if you feel it necessary, a small car can be used as a runabout. A motorhome is about 50 grand. A large new car is 25 grand and a large caravan about 15 grand, so getting close. Plus the motorhome will retain a grater value over time, just look at the 2nd hand prices. Most motorhomes average 7000 miles per annum and if you add up the costs over a year, you might be surprised at how little the difference is.
Anyway, as mentioned it is a personal choice and having owned both caravan and motorhome I am probably biased, but the sight of a bigger Yank tank is getting interesting again??