I liked Duo, I used them regulary for trips BHX-GOT, good price and good service. However one time I went to book and the route had gone without notice. It turned out they were in a pricing/route war with City Airlines, a GOT based company, who the GOT companies booked with to support local industry and the route became unviable for DUO.
Next thing, only City Airline/BM code share operated the route, normal pricing became £500 GBP regardless of how far in advance you booked.
Shame.
The staff were very good :-(