The CPO programs are extremely accurate and fast. They have been called the 'gold standard' of electrostatic electron optics.
For a recent description see the paper: Achieving the highest accuracy with the BEM, by F H Read, Microscopy and Microanalysis 21 Suppl S4, 182-187 (2015).
The method of calculation used in the CPO programs (the Boundary Element Method) is almost always much faster and more accurate than the traditional methods used in most other programs. The only published comparisons that are known to us are two papers that show that the CPO programs are typically two orders of magnitude more accurate than those using the traditional methods. A very unusual feature is that the CPO package includes a large number of 'benchmark tests' that demonstrate the high accuracy.
The accuracy of the final results is of course of paramount importance. It is not a 'given' that a commercial program is necessarily accurate, although some programs do seem to want to give this impresssion. A valuable (and unusual) feature of the CPO programs is that the user can choose some of the accuracy levels. This enables the user to choose a low accuracy for the early stages of a study, to give quick results, and then proceed to the highest accuracies for the final results. Accuracy and computing time are always closely linked. This feature also enables the user to assess the actual accuracy of the end results.
To achieve the highest accuracy in the available time the user needs to be careful in choosing several different things, such as accuracy levels for charges and rays, segment subdivision levels, number of cathode iterations, etc. Here is a list that will help. (There is sometimes some overlap in the material, for which we apologise.)
For the accuracy of the charges and fields see the users guide, chapter 2, section 6.
For the accuracy of rays (trajectories) see the users guide, chapter 2, section 10.
For choosing subdivision numbers see the users guide, chapter 3, section 4.
For cathodes see the note on controlling the accuracy of cathodes.
All of these links will lead you to more detailed information.