Hi, I haven't used one for a half dozen years or so, but over the years, I've used dozens of Macbeth, and later Xrite machines at the place where I worked.
I agree that the older Macbeths might be repair headaches, but can't say for sure. I'd personally try to avoid the oldest using PMTs (they have a removable round filter turret facing front). I'm just presuming that the electronics are really old tech, but not much real basis for this. I do know that older units had a row of pots in the back (inside); these were interactive adjustments for the machine's linearity; if someone has randomly tweaked any of these... well good luck!
My preference would be something like an xrite 810, which reads R, G, B, and V(isual) all simultaneously. But I think replacement lamps may be costly, so make sure it all works first. You'll need instructions to calibrate it, as well as the test plaques. Since it does both transmission and reflection, you need both plaques.
Those would be my preferences, maybe not the best choice, but the ones I'm most familiar with. The Xrite 810 was one of the workhorses of the earlier days of one-hour minilabs. Id really say that operating condition is probably the most important thing, as well as having calibration plaques. I wouldn't want to pay too much, knowing that in the event of failure it may not be worth trying to repair. Best of luck.
Thanks, Mr. Franklin.