As usual, there's pros and cons, and talking about just one side causes bias. Yes, a PLB can work with more obstructions like trees. However:
With PLB, satellites can't accurately measure where the PLB is; the search and rescue crew will find you by local radio reception.
With a satellite messenger, the gadget knows its own GPS location to a pinpoint and can send that as part of the SOS signal. And you can text the SAR staff and say "I fell and I'm now stuck on a tall ledge halfway up the cliff".
With PLB, satellites can't accurately measure where the PLB is; the search and rescue crew will find you by local radio reception.
With a satellite messenger, the gadget knows its own GPS location to a pinpoint and can send that as part of the SOS signal. And you can text the SAR staff and say "I fell and I'm now stuck on a tall ledge halfway up the cliff".