One disatvantgae of not open-sourcing is that you loose potential bug finders and coders to help grow your product. If you think your product is mature enough and not too complicated, this is not a problem. But if you take a look at the tech world, a lots of essential tools for our jobs are open source because the community is a powerful way to make a product more robust.
Tackle it by how you feel, your current financial situation and available time.
Starting and running a business is hard. You'll need to dedicate time and even money to get going. You'll also have data concerns if reading personal information.
Open source can be exhausting if you're maintaining a popular repository (even if not popular... users find amazing bugs).
Both are rewarding and improve your life experience. However, one is definitely less risky.
Thanks for your advice Matthew, you're certainly right about how time consuming starting and running a business is.
One is more about making money and offering a solution in a black box, the other one is more about sharing knowledge while offering a solution.
I'm literally at this point myself. However, why not do both? Open source it, but make your company off of it? I don't see why you can't create a service that uses it, such as a website that charged a monthly fee to use your api... which the backend code is running off the open source code. I don't feel that is wrong. I mean if you look at pretty much any company that makes money in the tech scene, they use free code some point in the source code. But don't expect to tell others not to use it to make money, if you are going to open source it. That just wouldn't be fair.
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