I do not hav any additional info on the origin of this microphone.
The microphone is an omnidirectional miniature mic. It sits in a metal housing and mounts on the violin through the tailpiece G-string hole by the sue of a small finger-screw.
If you have a tailpiece with built-in adjusters you can either put a metal washer and mount the microphone between the G and D string or you can take out the adjuster-screw on the G-string and mount the microphone in that hole.
Here is a sound sample of the Mässbacka microphone trough my AER alpha plus amp:
You can see my eq settings on the amp below. I have not added any reverb.
Here is a sound sample going straight to disc: