The retention system is usually linked to the type of helmet; helmets designed for racing (on/off road) often feature a double D fastening device, while helmets dedicated to touring or urban commuting more frequently have a micrometric buckle. In reality this is not a rule, simply common practice.
For example, helmets designed to be used on race circuits or tracks require a double D fastening device, which is considered less likely to accidentally unbuckle. On the other hand, helmets that are more intended for tourist use, such as the modular, flip-up, jet or demi-jet helmets, often use micrometric buckles, as they are more straightforward and more practical to use.
Both systems are safe and in line with the Highway Code and can be personalised and adjusted to perfectly adapt to the consumer.
In any case, the most important thing is to fasten your helmet. Unfortunately these days you still see many people with their helmet on, but unfastened! For Airoh safety is priceless.
Wearing it without fastening it correctly is like not wearing it at all! In the unfortunate case of an accident or an impact, the helmet can in no way do its job and insurance will not cover any damages! Without mentioning the civil and criminal penalties to be incurred.