The May / June 2013 Australian Flying magazine has a 5 page write up on PLB's, discussing
The change (121.5 to 406 MHz)
The technology
Beacon Categories
Emergence of PLB's
ELT Concerns (for aircraft)
Value added products (spot etc)
Communication (registration)
Information on six units from 4 different manufacturers including device weight (for the gram counters)
The article may give you an idea on what unit to purchase
Regards Overlandman