There is an ongoing issue with [Manufacturer 1] headsets. These headsets are woeful. They have a tendency to fall off your head easily, under minimal acceleration, particularly relevant in a rejected take-off (RTO). I know of other ASRs filed by colleagues where this has happened during the take-off roll. However, another major issue is the mismatch between listen and talk levels – this seems to be worse on aeroplanes where one side is fitted with the older (better) [Manufacturer 2] headset and one side is fitted with newer (dreadful) [Manufacturer 1] headset. But it is also an issue with both sides fitted with the new [Manufacturer 1] headsets. I believe this to be a serious flight safety issue.