If it is just for monitor calibration, use a colorimeter like the ColorMunki. If you want to calibrate your printers and everything else under the sun, get a spectrometer like i1. The concern with a used spectro is the age of the lamp, they go out of calibration over time and with use. I would find out the cost to recalibrate / replace the light source before buying a used one so that you know you are not going to spend more than a new one. All of the units you mention should have no problem calibrating your monitors.