If you regard Air Berlin as a low cost carrier this is the best you could experience in this segment - planes are clean and pretty new. You get good attention onboard and a snack plus a soda or juice for free. On the ground however the experience is different. They are really overdoing it with baggage weight I find it a sure way to turn a loyal customer - holding the Frequent Flier Card - off by making a big fuss (happened twice) when the baggage weighs 215 kg instead of 20 kg. Terminal at Berlin Tegel Airport lacks seating which becomes pretty inconvenient if a lot of delays occur at the same time. If the price difference is not more than 10-15% to a regular carrier like LH or CX I would probably pay that and choose them instead of Air Berlin.