boqurant
Contributor
Another vote for the Nautilus Lifeline - it's cheaper, easier, and I think it's more useful in more scenarios (including being washed out to sea) - and triggering it in near-shore, easily-solved situations doesn't need to involve the coastguard 
In the washed-out-to-sea case, if (if!) you're diving with a halfway-responsible buddy / dive guide / dive operator, someone _should_ notice you missing at some point, and someone should mount an S&R mission within 24hrs, either directly or via the coastguard, and they will be listening on VHF16.
Obviously you're already carrying a DSMB and whistle (if not, why not), and it's simple to also carry a signal mirror, and for extra brownie points: fluorescein and a(nother) strobe (the Nautilus has a strobe).
<edit> I'm not against PLBs of course, safety measures are subjective and a personal decision!

In the washed-out-to-sea case, if (if!) you're diving with a halfway-responsible buddy / dive guide / dive operator, someone _should_ notice you missing at some point, and someone should mount an S&R mission within 24hrs, either directly or via the coastguard, and they will be listening on VHF16.
Obviously you're already carrying a DSMB and whistle (if not, why not), and it's simple to also carry a signal mirror, and for extra brownie points: fluorescein and a(nother) strobe (the Nautilus has a strobe).
<edit> I'm not against PLBs of course, safety measures are subjective and a personal decision!