While it's cool that you are making headway, a better question is: does this financially make sense in the long run.
While it's cool that you are making headway, a better question is: does this financially make sense in the long run.
Given that context I think any paying customers / level of profitability is a success. Yes, you can do lots of math about cost of time and opportunity cost but that ignores the original intent behind the project.
I played around with the tool a bit and it's actually pretty impressive--really solid for for a one person team and I wouldn't be surprised if it gains more users.
I would also argue that getting 40 paying customers is pretty decent validation, and the author can now spend money on marketing if that's the direction they want to take it.
This calculation doesn't make any sense. Can you build the initial Google project in your spare-time? Probably, if you find enough qualified volunteers.
Does that mean it's a viable business?
Absolutely not.
You need to check how much you would have get paid when working in your last highest paying job... (Even when you do things in spare time)
If my alternative is sitting in front of the TV, or reading a book, or gardening, or... whatever but I choose to do something like this, the cost of that time is effectively zero because that's what I would have been doing with it otherwise.
So, by "working" at something I enjoy and that I'm doing by choice, I'm basically being paid to entertain myself.
You have to distinguish between a hobby that brings you pleasure and the beginning of a business that will earn a profit if you valued your time at its opportunity cost.