And this is why I will never pay for software
There is a reason why I have never paid for a piece of PC software in my life, and in all probability will go to the grave without ever having done so.
When you pay for software, you have neither the right to modify it to suit your requirements, nor the ability in extremis to take that right by force. You are entirely beholden to the supplier's whims and caprices. They can charge you more money if you want to add more users. And at any time, whenever they decide, they can render it obsolete by altering the formats in which data are saved; so anything saved out of a newer version becomes incompatible with your version.
When you use Open Source software, you -- or any competent programmer -- can study its operation and adapt it to your own requirements. You can make as many copies as you like, and the only limit on the number of users is imposed by your hardware. Upgrading to a newer version need not cost any money. If data formats are changed incompatibly and for some reason it is not possible to upgrade to a newer version of the software, or upgrading would require other software to be upgraded, it is possible to write a separate program to translate between "new" and "old" formats.
Until paid-for software comes with the same freedom to study and adapt it (even without the freedom to share it) as Open Source software, it really isn't a hard decision to make.