I might however be interested to add "something", preferrably open source, perhaps running on a RasPI or so, to display nearby ADSB transmitting planes.
...Flarm I will not touch even with a barge-pole - it is not under any formal norm or control, bases upon the cheapest consumer electronics, and is partially non-open.
Make up your mind Jan, are you going with 'cheapest consumer electronics' or not? (Not that Flarm is, actually, that).
But more importantly, in the UK at least, probably 75% of gliders flying cross country carry Flarm. If you want to see them, that's what you need. You might wish they carried something different, but they don't.
Paul