ATC is an aid , not a cure all for incidents.
The most important aspect of safety is correct loading, the correct tow vehicle, correct tyre pressures and correct driving style.
Reading the road both ahead and behind is essential to keeping safe, and driving within your capability, and that of the prevailing conditions.
ATC can be retrofitted either by Al-KO or one of their approved agents.
Once fitted it is not switchable between off and on, it is ON when the car is connected.
Is it worth the extra cost? purely a decision on whether it makes you feel safer, which can actually be detrimental, bearing in mind the info above.
In most cases it may only be known to activate maybe 1% of the time it is active, and most likely at slow speed going around a roundabout ,, or has been found, travelling over roadworks.
It is another gadget which is likely to give problems at some point, most do.