Question to those who are equipped with a "traffic and collision avoidance" item, what is the percentage of General Aviation aircrafts in Europe that emit in ADS-B out... and so that we could see with SkyDemon (with Pilotaware for ex.)?

I would suggest that less than a 1/5th of aviation traffic has ADS-B out here in the UK (see the FlightRadar24 stats). I have two traffic systems in my 1979 C182. A TRX-1500 which provides for FLARM and ADS-B detection and presentation, and also Mode C/S proximity warning, but all on the tiny Garmin 650 display. I have an I-pad mini running SD fed by the Sky Echo 2 which provides for a much better presentation of ADS-B traffic on (the larger) screen but no FLARM (separate fee which I don't seem to need on my TRX-1500) and no Mode C/S warning. As a result I would not recommend purchasing the Sky Echo 2 unless the connected software is capable of making use of Mode C/S information and providing some sort of warning.