Myanma Airways and Air Bagan also have ATRs. Infact some of Air Mandalay's ATRs are now with Air Bagan.
Air Mandalay now only have two ATRs in their fleet. Until recently, they were French registered, but now they've reverted back to local "XY-" registration (and all that entails with that!). Be aware that flight schedules by Myanma Airways can change at short notice, or even mid-flight! lol! This
webpage describes it perfectly.
I'm a frequent traveller to Myanmar and have always preferred to travel domestically by bus!