Another factor in the performance of digital callipers or any digital scale for that matter is the batteries. For any given size and voltage standard, there are two types of battery chemistry available, alkaline and silver oxide. Both are fine in the suitable application, but the silver oxide has a much more stable voltage characteristic, so is preferred for measuring type applications. I know that the first sign of low batteries on my Measuremax instruments is poor repeatability of the readings, and the silver oxide work well for much longer than alkaline batteries.
I don't know if the top quality instruments have circuitry that compensates better or are just normally supplied with the silver oxide type anyway. I am sure that better batteries will not bring a cheap device up to the quality of the better instruments, but they reduce some of the frustration in the range where they are adequate. It may be worth trying a better battery before consigning them to the bin if you have already bought them. Of course better to buy the best you can afford rather than the cheapest available. But for final cuts and best accuracy, I am another who resorts to the traditional micrometer, a beginner lesson learned the hard way.
(The alkaline ones are fine for less critical applications, such as LED lights and music devices, but the voltage drops off with use more than the silver oxide, so not good for accurate measuring instruments of any kind.)
MJM460