I love how smooth the shutter feels, how little vibration it has, and the very bright, sharp and large magnification viewfinder is (better than the LX IMHO). Once installed with a newer brighter screen, manual focus is a joy (trying to manual focus with Pentax cameras since the Z series is a torture
). However, the MX is getting very old and many with aging shutter timers which are unable to hold the accuracy. The top is also too prone to dent imho. The ME Super has the same high magnification viewfinder too, but its screen is fixed and dim, and I hate fixed screen because the trapped dust cannot be blown off. But being the most successful camera at the time, Pentax did many things right.
The Super A/Program is the most feature rich manual focus body Pentax have ever made. I had a few in the past too. But in practice, the push button is awkward and slow to use, the focus screen while removable, it is dark and not interchangable. Mated with smaller magnification, manual focus is more difficult than the MX. The shutter/mirror is also very noisy with most vibration. I tested the MX & Super A on a rigid tripod with FA*200/2.8 & FA*300/4.5. While the MX was able to produce sharp images, images from the Super A suffered from vibration. Another way to test is to put a glass of water on the prism, fire the shutter through timer and observe how the water vibrates. Would be fun.