Oftentimes, what appears to be a bug turns out to be user error.
When the Pro plugin is properly installed, there should be no limit on users.
If there is indeed a bug in the software, prior to opening a claim with PayPal, a bug report would be courteous and helpful. I will gladly resolve any issues when given an opportunity. Reporting bugs helps improve the software and helps others who may be experiencing similar problems.
Although my policy on refunds is clearly stated in the license and on the Pro plugin purchase page, I have issued refunds in the past, when I felt a refund was merited. I have also been known to add extra features to the Pro plugin, at the request of buyers, for no extra charge.
Sure, if you are a developer, you can code your own plugin. How much is your time worth? $30? More?
If anyone needs an example of my work prior to purchasing the Pro plugin, User Meta Manager is available for free. The Pro plugin simply extends the capabilities of the free plugin.
Have a nice day. :)