Someone said all PLBs are manually activated, which is no longer true. There is a new auto life jacket with an integrated PLB which is being actively promoted by BIM the Irish government fishing body particularly at small fishermen. You do their survival course , cost about €150, and you get a free voucher for a life jacket worth about €700.
Details here http://chmarine.com/acatalog/mullion...150n-3mvi.html
Share with any commercial fisherman you know in Irish waters because way too many are fished out dead after going overboard hauling pots or nets solo.
As for their efficacy, a very safety conscious young fisherman I know went overboard about four months back. He was fishing with a crewman in a bit of a swell and about to drop a string of pots with an anchor attached. The anchor was sitting on the gunwale ready to be pushed in but slipped off with the swell as he stood by. The fluke went into his oilies and took him over the side. He'd done the BIM course just a month previously and was wearing the new Mullion integrated jacket. It inflated perfectly and then it took the two guys about ten to 15 minutes to get him back on board by which time they were both exhausted. Less than 15 minutes or thereabouts later the RNLI arrived alongside while the two lads were still recovering from the shock and exertion. The PLB triggers when the jacket inflates and had summoned the cavalry.
Amazing bit of kit and had my friend been fishing on his own he would most likely have died from hypothermia even though he's religious about life jackets. Full credit to BIM for both the jacket and the initiative, it will save lives.
For myself, as I'm mainly solo, I ensure someone knows where I'm going and when I'll check in at two/three hour intervals. I have a fixed VHF and always carry a floating hand held in my jacket. I carry a waterproof phone and while I have always carried personal flares on a lanyard, I've dispensed with those in favour of a PLB on a lanyard. I never had much faith in flares in remote spots anyway and there is a limit to how much stuff you can carry on your person. I place little value on anything in or attached to the RIB because on at least two occasions in my experience I've been extremely lucky not to get flipped and if that happens you won't be getting at anything in the boat.
If I had to choose one thing, it would be the PLB as I see plenty of areas where vhf is useless with high cliffs or no traffic in line of sight and phone coverage can be very sketchy inshore. With a six year battery, there is no maintenance and little to go wrong so maximum peace of mind. If you haven't got one, buy one , works out about €40-50 a year even if you throw it away rather than replacing the battery!