I remember years ago looking at a MR ARM in a shop and was amazed at the tooling marks and lack of a nice final finish on the receiver. Reminded me of a rifle produced during war years. (Israel is constantly at war.) Through the years I saw other MR guns that were finished nicer and when I finally bought a IMI rifle, which was a AA, the finish work was exquisite. Almost perfect, the only other military style AK that compared in final finish work was my Bulgarian Arsenal rifle. I've seen some references concerning AA addressing tool marks and selling rifles where these issues were corrected. As mentioned, the early MR guns lacked firing pin springs and had different flash suppressors. In the practical sense they're both desirable.