I am splitted between, rewarding the good work, and contributing to the open source ecosystem outside your daily job.
In one hand, all your efforts should be rewarded, because this is mostly time you took over family weekend or working out or taking care of you, and for the service offered.
On the other hand I guess if you make the month with your primary job, you might have used open source tools in your business project, and so giving back is not a bad thing too.
I am more of the second group, I used so many great packages that made my job easier, and giving back is so great at the end of the day. And for me personally, if this stay side project, I know I could never bring this business proof quality to my projects so I would never dare to make people pay for my side projects.
I guess if the offer is fair (like a freemium) it is OK to make people reward you for the good service.
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