I am not particularly an exponent of the devices but as an occasional designer of electrical installations it would be reckless of me to ignore a recommendation in the national standard.
421.1.7; "Arc fault detection devices conforming to BSEN 62606 are recommended as a means of providing additional protection against fire caused by arc faults in AC final circuits". Under a note that follows the regulation there is a list of situations that might benefit from AFDD deployment, including sleeping accomodation. So if I was designing the electrical installation in say a care home, AFDDs would be on my spec!
Schneider have developed a double module unit ( twice the width of a single MCB) which combines arc fault detection in both series and parallel modes, RCD and over current protection. The initial costs will be in the order of ?120 which will quickly tumble as competition increases.
Whether they will catch on or not remains to be seen but I think it would be unreasonable from a fire safety perspective to dismiss the benefit of the incredible technology employed in these devices.