As Shawn points out, “..reference of progress..” is what we should be looking at. Without getting technical, accuracy is important, but at the end of the day it boils down to consistency with methods used and the progress from one assessment to the next. I have successfully used my Slim Guide Calipers for many hundreds of clients showing their progress. Find a device that suits your budget and use and then get to know how to use it.
Tanita has software that connects your device to your pc allowing you to automate and streamline your assessments, they also include a nutrition side to the package which may interest you.