I'll continue to post some thoughts on the M500 / M500-384 and the EMT2 (Pro) in this thread. These mics are small, but powerful and are surprisingly often mentioned in serious bat studies. According to the Pettersson website, the M500 and M500-384 use "the same advanced electret microphone technology as the well-known D500X detector". And cost only a fraction of the D500X.
Someone has posted a sample file
recorded with the M500. The BatExplorer 2.0 rates the quality of the recording as "99%", clearly superior to bat call files from my Ciel Micro Trio (rarely rated higher than 55%). The BatExplorer 2.0 documentation defines "Recording quality" as "probability that the recording contains bat calls."
I haven't found a sample file of a bat call recorded with the Echo Meter Touch 2 (Pro). If an EMT2 owner could post such a file, it would be great. Not the ideal time of the year for recording bats, I know...