Must say I was a disillusioned to find that PLB's are not exactly fire and forget.
They seemed to be a better bet for someone who finds themselves stuck up a mountain with a broken leg, than the poor sailor, struggling to stay afloat in the middle of a storm.
If you're going offshore, a proper EPIRB seems a better way to dispose of beer vouchers,
We carry a couple, one main floating one for RS and a second handheld one with GPS fix, both of devices are ACR bought from US chandleries and re-programmed for nought by ACR for use in the UK.
We used the hh for trips in the wild in Norway and would take it with us in the l/r, should that day ever come....
A PLB will need to be held clear of the water at the correct angle for around 40 minutes to identify the beacon's position using Doppler shift analysis. This is helped by incoporating GPS data in the 406 burst but you will still need continual 121.5 transmission for homing once the local SAR service are deployed. A full size EPIRB is designed to be most effective when floating using the water 'ground' to boost performance.