I do not know anything about the MD600 from personal experience, only a few passing comments from friends and colleagues who have operated them and the 520. Never heard anything good about them.
I would qualify that statement by adding that I think that the Hughes/MD/Boeing/MDH (whatever) products I have had the misfortune to operate are the most labour intensive, unreliable, expensive and poorly supported product from any manufacturer. I wouldn't have another one if you gave it to me for free!
I would like to know if the points raised by the GAO report on the INS MD600 purchase were remedied? I found many of them to be equally applicable to the MD500 series, and the majority of those deficiencies had been around for decades, not the short term.
GAO site
Enter MD 600 in report search.
Apologies for the difficulty in accessing this report. Can't get the UBB code to work correctly.
Edited for new software