*Absolutely sure...otherwise the rescuer's could waste a lot of time trying to find you without the homing signal.* Not all EPIRBs/PLBs have GPS.
Scott you are correct the PLB's do transmitt on 121.5 as well as 406. I called a local dealer to confirm.
The local dealer has the ACR Aqua-link + on sale for $260 with a $50 rebate. The cost to replace the battery on my EPIRB is $285.
The difference between an EPIRB and PLB is the size of the battery and the EPIRB's ability to right itself and transmitt when floating. Otherwise according to the dealer they are exactly the same.
I'm going to buy a PLB and keep the EPIRB, the battery still tests good.