Apologies Tim, I read in more posturing than was obviously there.
Clearly you are aware of pilots who, to reduce cost, might seek marine
systems to carry in their gliders. This hadn't even occured to me.

One point worth revisiting, however, is the intent of SARSAT to cease
121.5 support in 2009. Another point is the use of small, cheap,
personal 121.5 ELTs, typically strapped to the parachute. My
undestanding is that these are all manually operated. As a vendor, you
must satisfy demand for such devices, but they clearly suffer the same
disadvantages you noted for GPS PLBs, and offer none of the benefits
of accurate positioning or timely interpretation of signal.

For years we've heard proponents of ELTs cite them as lifesaving
devices. In any accident which causes serious injury, the first hour
is absolutely critical to survival. If we are going to discuss ELTs as
pilot safety devices, then we need to differentiate the choices very
carefully. If we instead view them as search (but not necessarily
rescue) facilitators, then we have more latitude in our choices. As
for my own research, a 406 ELT with a coupled GPS seems the best (and,
of course, most expensive) overall solution. I would also be tempted
to have a GPS PLB on or in my parachute. As I would carry such a unit
for sailing or back country skiing/hiking, it seems a reasonable added
expense.