I did 2 short term (6 months) one-to-one Chinese language courses through Xmandarin while living in Qingdao. The teachers were friendly and professional, I really enjoyed the classes and my Chinese improved exponentially during this time.
My requirements were a little bit different from most students as I am working full time and, in this regard, I am extremely happy with the teachers as they were able to tailor lessons to my specific needs. The majority of classes were spent preparing for my HK4 exam, but there were many classes where the teachers helped me prepare for presentations that I needed to deliver in Chinese. These were invaluable! The school also arranges regular activities and these are a lot of fun - cocktail making classes, Chinese calligraphy, group trips to good places in the city.
As for Qingdao - I love this city! And the school has a very central location close by many coffeeshops, bars and restaurants, plus a nice walk away from the ocean.