Oh great, so now I can fly from Saarbrucken to Kassel! That's handy! Seriously though, if it's cheaper than the Deutsche Bahn then it would be worth considering.

Kassel airport seems to have an uncertain future, I recall reading somewhere that it operates with a huge loss. Last summer OU was offering flights to Split and, despite the distance from Oberhausen, I was tempted to try it but didn't have enough time in the end. The other flights of vague interest were some destinations, such as PMI, with Germania.