I have a general idea regarding what they are doing. And there probably are some technical reports available on the Web.

My guess would be that these signals are probably among the more reliable of the earthquake precursors. But the signal intensity for a given approaching earthquake would likely be quite dependent on fault zone factors such as the type of rock in the fault zone, the type of fault zone, if it is out in the ocean or inland, how deep it is in the crust, etc., and the earthquake magnitude of course.