With my airplane I supply life jackets, a raft and a GPS PLB.
Now here is the catch - if I rented someone else's airplane I would take my kit with me - I know its history and that it works - would one trust other people's kit?
That said the PLB is registered to me and my plane - but something is better than nothing (my airplane is US registered and operated in the eastern caribbean) - if it breaks the rules I'll suck it up.
This is in addition to the normal airplane ELT (it wouldn't work long if at all as 95% of my airplane's time is spend over the ocean.
PLB's are a good idea and they will bump up the chances of being found quickly - ideally have your own but if it comes with the airplane so be it - I do hope that someone outlaws the practice of charging for the "rental" of safety gear.