I just received my Stratux unit from Crewdogelectronics for which I specified I needed the European version and with FLARM, meaning it should be pre-installed. 

I have connected the unit on the ground selecting GDL90 Compatible Device under Third-Party Devices (tapped "go flying"), but only seem to be able to see large airliners heading above and not sure I am getting any FLARM readouts. And even the airliners show intermittently for a few seconds only to disappear / reappear at irregular intervals. 

Also, is there a range beyond which you cannot see ADS-B/FLARM returns? 

Then there are a number of aircraft I can see on FlightRadar24, but are not showing up on Skydemon even though in Stratux I have selected to see all a/c up to 40,000ft.

Anything I am missing here? Many thanks for any enlightenment, especially re. FLARM.