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.
Reserved seats?: Lately, some bargain airlines started selling "reserved seats" on the plane. However, the seats are all quite similar and even if you don't reserve a seat when you book your ticket you will still be able to choose your seat when you board the plane or you will be assigned one at the check in desk. So you can easily avoid paying extra money in order to reserve your seat.