AirServ (no 'e' on the end) are stable, well funded and pay well for the level of pilot they accept and the work that they need doing.
I see you are from Belgium which means you speak French ? This could be a great asset as much or their work is in West Africa.
Like any NGO there are some pleasant committed people and unfortunately some fanactical sociopaths who cannot function in the 'real world'. Some of their management and pilots are somewhat difficult to work with, to say the least but what easy going people volunteer to operate in the real sh!tholes of the world ? Be prepared for lots of politics and apparently weird ways of running an aviation company. They have their own agenda.
Much of their work in Africa and the Middle East (Baghdad and Kabul) is contracted out to Naturelink, a South African company, although they have their own operations too.
Religion is not a requirement but an acceptable measure of morality and maturity is, but with that strange twist of North American hyopcracy.