The first thing to look is GPS compatibility; this is the device’s ability to send out your exact coordinates as opposed to waiting for the satellite to do that, which will only waste precious time.
Self-test is a good feature as it allows you to test beforehand whether the device is working as it should. However, keep in mind that this can also drain a lot of the battery so should only be done a few times over the life of the PLB.
Check the battery life. This can be divided into two parts. Firstly, how long the PLB charge will last when the equipment is not in use, and secondly, how long the battery will last when transmitting the signal. Both durations should be as long as possible.
Operating temperature is an important feature to look at as you may find the need to use the PLB in remote areas with extreme and harsh temperatures.
Performance in water is also an important factor. A lot of PLBs have the ability to float in water as well as be water resistant in case you’re using them in or near a watery environment, but some models don’t offer these features so check this out before you buy.