I would say 'similar performance' rather than same; I don't have any figures for the DS4 (or Flight for that matter), but Apeks ANSTI testing on the DST/XTX50, for example, shows Work Of Breathing as 0.85 Joules/litre, compared to 0.41 on the FSR/XTX200. Of course both are very good and well within the 3 Joule maximum required for CE certification