will float in the proper position, and the antenna
is fixed in place. It can be configured to trigger automatically when released from the holder. Some EPIRBS will automatically release when submerged.
A PLB may not float without a flotation cover. It has to be manually activated, and the antenna manually extended. You have to hold or otherwise secure the PLB in the proper orientation for the antenna to work as designed.
An EPIRB has a strobe light and a battery to support 48 hours of on-time.
A PLB *may* have a flashing LED, but many don't. The operating time is 24 hours.
EPIRBS and PLBs both transmit at the same power level, on the same frequencies.
You can carry a PLB on your person. An EPIRB is big, and goes on a bracket or in the ditch bag.
EPIRBS are definitely more expensive than PLBs. I assume that production volumes and market demand are the price factors.
Here's a link to ACR's EPIRB/PLB comparison: http://www.acrelectronics.com/media/...0V%20EPIRB.pdf