Hi, personally, I found the KA version less reliable, because often the contacts were just a tiny bit off and didn't make proper contact. It sure freaked me out when suddently I couldn't take a photo. I threw it out afterwards. Having to rotate the lens a bit on/off to be able to get a photograph is not my idea of good design...
The plain old K is the best, both mechanically and without exposure quirks because of bad contacts. However, when opting for the plain K, you obviously lose some functionality especially on IstD/IstDS... And do get either a return policy or get it very cheaply. I have had few cases of lenses and adaptalls being badly compatible...'twas the Nikon adaptalls, but I believe some compatibility quirks might be with other versions as well. Otherwise, there were some excellent lenses in Adaptall mount. Frantisek
