There are several good reasons for going to 406mhz, the best being that the COSPAS/SARSAT support for 121.5 and 243.0 is being phased out. If you have a 121.5 or 243.0 beacon at the moment and set it off you will have to wait for at least 2 satellite passes before anyone gets alerted due to the number of false alarms on these frequencies and the need for 2 different indications to resolve doppler inaacuracies, plus the satellite has to be able to see an earth station to transmit the info to it.
A 406 beacon can give a unique code with all sorts of embedded information (including GPS coordinates if fitted to it) so as soon as the signal is received people know who you are and where you are.
Homing to 121.5 and 243.0 is primitive at the best of times - it is much easier to set up a search and rescue when you know the lat and long of the survivor.
http://www.cospas-sarsat.com/FirstPa....5PhaseOut.htm