My best advice for anything rocketry related - is testing, lots and lots of testing.
I think many issues with Altimeters, RF trackers, GPS locators ect. are sometimes caused by user error.
For things like altimeters, trackers, GPS locators and such, these can all be tested:
-Ground testing. (For GPS -one person hides the rocket, the other person finds the rocket)
-Flight testing. (Fly the GPS system several times on "low" flights where you keep full visual recovery) Make sure the GPS reports the correct coordinates.
Testing accomplishes two goals. It helps to make sure the system is working, and it helps the operator understand the system and how it works.
I personally have never failed to find one of my Eggfinder equipped rockets.