I had 3 flights with eznis - from Buyant Uhaa (ULN) to Murun (MXV), from Murun to Dalanzadgad (DLZ) and back to Buyant Uhaa. As a result I had 2 flights delays for 6 hours each (so, the whole day was lost which of course affected my travel plans). Very poor English of the staff even in head-office and nobody knows what is going on. The third trip from Dalanzadgad to Buyant Uhaa wondered even myself. They moved me and my wife from the 9 am flight to the 5 pm flight (most likely to fit into the plane an organised group of tourists) and I found it only when I was trying to check in. I would recommend this airlines only if you are happy to lose 3 full days of your trip and stuck in the middle of nowhere for a day or so. Onboard service however is good enough.
Food and drinks on the plane: One of the most important "features" of low cost flights is that the airlines do not offer free food and drinks on the plane. Food and drinks are sold on board, but they are quite expensive. If you travel on a low budget you should take some sandwiches from home. But remember that you cannot carry any liquids in your hand luggage past the security check!