Hi Neil, I bought one so that I know I'll always be in compliance. And in fairness, the fact they run continuously for many hours is a big plus. But I am keeping my old flares, especially SOLAS flares. From personal testing they almost always work even if long past expiration date, and the link below is a report from this board on the relative brightness of the SOS device vs SOLAS flares. SOLAS is more likely to get attention.

http://cruising.sailboatowners.com/cgi-bin/bbs62x/webbbs_config.pl/page/1/md/read/id/216423