I bought 2 Zone VI Pentax digital spot meters back in the Fred Picker days. They have had an easy life, but have now drifted to be 1+1/3 stops apart (and 1+2/3 stops at high light levels) and neither is within a stop of many other meters which all agree with each other (Minolta spot, Nikons, leica m6 etc). I just adjust the film speed to get them to agree with normal meters. But I agree with the ergonomics and the readout: the best!
I have read the info from Paul Butzi and I wonder if the Zone_VI mod is particularly useful (The Zone_VI mod was advertised as making readings through filters just right with one film only: Tri-X sheet film). I also wonder if the Zone_VI mod is the cause of my drifting readings.