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.
Weigh your luggage at home: Avoid excess baggage charges by weighing your luggage at home and trying to stay under the weight limit (15 or 25 kilos per checked-in bag, depending on the airline). If you exceed the weight limit, you may be asked to pay 10-15E per extra kilo. If your luggage is overweight and you can't leave anything else at home, it may be a good idea for you to take a hand baggage. But be careful: you need to check the weight limits for your hand luggage too!