http://braukaiser.com/wiki/index.php?title=PH_Meter_Buying_GuideI think this is the resource you might be looking for. Kai is quite helpful, and would suggest his three part series on understanding pH on that same website.
I had assumed the mw101 was the new version. its getting some crappy reviews on amazon. dunno if its rivals talking poorly about someone elses gear. all the pH meters seem to have a 5050 feedback