Message received via email and posted here for others to learn the answer:

I’m going to try JUser BestBefore standard, but I cannot understand what “Process IDs under 42” means and I could not find any explanation in your site. Will you please help me?

Answer:
The explanation is in de documentation that comes with JUser BestBefore:

PROCESS IDs UNDER 42?
Joomla! only creates user accounts with IDs 42 (admin) or higher.
Some third party extensions, we take Community Builder Enhanced (CBE) as an example, create a user account with user ID 1 and username 'Message Bot' or alike. Such user account may be necessary for the extension to function correctly. Therefore you can have this type of user accounts excluded from disabling or removal by the plug-in (this is the default setting).