I have looked into these. Don't yet have one. From what I can tell the PLB, SPOT, and InReach will transmit your GPS coordinates to rescuers and/or folks at home, but won't give them to you. Is that correct? To me that seems very odd as it would be trivial to build into such units. Mostly what I would want from a GPS device is my location. Navigation I would rather do with map and compass. I guess I too am waiting for one device that could do everything I need.
BTW, not sure it was made clear, but another difference between the PLB and the SPOT/InReach option is that with the PLB there is not fee for service plans. Once you buy the unit, it is always ready to use with no additional costs. Also, the manufacturer says that if you ever have to use your PLB for a rescue, it will be replaced free of charge.