I spent one month studying and interning at Liden and Denz Moscow. It was a wonderful experience.
The classes are small - no more than 10 people, and the teachers are dedicated and interesting. They are sorted by ability based on the European Languages Framework (A0, A1, A2 etc.) There are classes from complete beginners to advanced users. The students are all ages, from all walks of life and all over the world, which makes for a varied learning experience. The work is hard, there is homework and the classes are intense, but this is how your Russian language improves so much in a short space of time. After just four weeks of classes I felt my Russian had improved a lot.
The internship programme at the Moscow school is remotely supervised, which meant that we had a lot of freedom to work on things which interested us, but that we could always speak to our supervisor via messaging/email etc. The experience was really useful for me as it allowed you to be creative and think about all of the ways that you can share your experiences of Moscow.
The school offers trips to visit key Moscow sights but there is usually a charge for them. They were usually good value and a good way to meet fellow students. I would have liked to have even more opportunities to socialise with fellow students through the school though.