Personal AIS Units
What is an AIS Beacon? - An AIS Man Overboard device is technically not a beacon as it only transmits a local signal using the Automatic Identification System.
This signal will not be received by dedicated search & rescue services and the signal will only be received by vessels that have AIS receiving units within a range of around 5 miles.
AIS MOB units are best suited to situations where the MOB can be recovered by the remaining crew of the vessel from which the MOB occurred. They're also useful in busy waterways as it is a requirement for most commercial vessels to run AIS. You can see just how many boats use AIS at websites like Marine Traffic
An AIS Beacon can also be used alongside an EPIRB or PLB to assist rescue services in pinpointing the casualty once they have arrived to the area of the rescue.