Firstly
Cale, there is already a wide variety of responses from members. VHF and PLB's (EPIRB's) are both primarily about increasing your safety margins when out on the big blue. I think some distinctions ought to be established between the usefulness and priority in their use, and then we can deal with the detail re MROVHCP licencing. Every reference hereafter, where the importance of licencing could be useful (clear communications) I will mark with a purple coloured (MROVHCP).
VHF ..... Allows line of sight communications between all similarly equipped stations, be it vessel to vessel, or vessel to Coastguard/VMR. (MROVHCP)
1. It is useful vessel to vessel (read kayak to kayak) for any communications. You may wish to find your paddling partner/report a capture. It may be useful to your mate to help land a big fish, or to determine his location/intentions (main use amongst kayak fishos).
2. It is useful for all updates from Coastguard/VMR, particularly in relation to the latest marine weather forecasts, warnings and observations.....(join your local Coastguard/VMR for a very small contribution). Coastguard/VMR are all sailors, boaters, even kayakers ... they fully understand, and like no one else you can contact, they understand the importance of safety of life at sea. e.g. if you are worried about a storm cell you have spotted/ a forecast wind change that has not arrived ... just call them. They will look at BOM radar/observations and will advise accordingly. They DO NOT MIND helping. (MROVHCP).
2. If something goes wrong, and it is a non-critical problem, VHF it is the best by far (over mobile phones) to contact people who are on the water, and capable of providing assistance. A mobile phone call will not get you assistance from someone on the water. This could be a mate in a yak; it could be a power boat 300 metres away; or it could be Coastguard/VMR if no-one else is close by. As it is a non-critical problem and is not threatening life, make a normal call. (MROVHCP
3. If something goes wrong, and it is a serious problem (which could eventually worsen), but it is not currently a grave and imminent danger to life, call "Pan, pan pan ..." (MROVHCP)
4. If something goes wrong, and it is a serious problem (or likely to develop into) with grave and imminent danger to life, call "Mayday, mayday, mayday...." (MROVHCP Try this contact on your VHF first, unless you feel you are about to die (in which case activate your PLB). That should get a response quickly, and is likely to evoke an emergency response on the water (as far as kayaker fishers go) faster than EPIRB activation.
PLB/EPIRB
To be used only when there is grave and imminent danger to life. If in any doubt use PLB/EPIRB (when the sh*t hits the fan).
As you can see, having MROVHCP is useful in many situations, by clarifying communications. This avoids ambiguity, at a time when things may be critical.
See your local Coastguard/VMR for the next course.