Sure, here we go.
I found a line in the file saying:
em28xx 1-2:1.0: Currently, V4L2 is not supported on this model
Surely, that cannot be good. Also, I activated trace debug for "config" and "dvb" in TvHeadend, and within not even a minute it produced a file of about 10MB (which was too large for pastebinit or an attachment here ...), but I could certainly cut that one down if there is interest.
Update: I just attached the stick to my Rpi3 running LE 8.2.0.1 (dmesg | paste; same message as above) but it works (more or less, quality is worse than with the XBOX ONE tuner, I would say).
Update 2: I also attached the stick to my Wetek Play (AML-8276-MX). Here, some picture and audio was visible, but in really bad quality not watchable; lots of blocks and discontinuities).