"I worked on this project during my free time (weekends, evenings, holidays) for approximately 12 months, from April 2018 to March 2019."
If by "free time" the author means 1h per working day and 4 per day on weekends, that would be ~680h -> 85 days (8h per day)(back to back). Not that's not a good ROI at least for me. I won't count the deeply unique value of "time not spent with family/friends/children".
I sincerely hope that this picks up and gets 4000 paying customers, but so far for a year's worth of work it's not impressive.