Daan,
As the manufacturer, we would recommend pipe pressure. My dad and I both always used pipe pressure and were able to reliably fly our Turbax DFs for years without issue (my dad especially). Don't get me wrong, there was the rare flame out from time to time, but most landings were with power on which is what you want. Just something to think about. You can email us directly as I'm sure my dad has even more insight on this (
[email protected]).
Chris