I've used them from Stansted to Glasgow. Better cabin service than EZY, but only two flights a day which is difficult in a high density market.
You get allocated seats, sweets and newspapers on boarding, drinks (soft), and a rather Germanic heavyweight sandwich/roll that all seem to have been made, pressed together and loaded at Berlin at 05.00 each day.
On returning into STN aircraft goes to international pier, pax are segregated at foot of steps, domestic pax into bus for terminal, continuing pax up into pier. The aircraft continues to Germany, there is a mini-hub operation with about 6 simultaneous departures, fed by arrivals from Manchester and Glasgow. For domestic pax it all adds about 10-15 minutes to the overall journey time.
A lot of pax seem to be connecting to/from other AB flights, they definitely organise it as a feeder with through baggage and boarding cards. Northbound all the through pax were seated in the forward cabin, domestic pax at the rear. The FA stood at the front and did the safety briefing in German, then repositioned to mid-cabin and did it again in English ! There's a lot of German spoken on board.
They need attention to how to keep on time. Lessons I am afraid EZY/FR could teach them.
For a new service with an operator "unknown" on the route loads were surprisingly good.
I'm guessing they will use a Fokker F100 to Belfast.