I was searching something like this to convert my maps, charts drawings in iPad to Obsidian. But 1 diagram/month is so not enough. Yes 3$ for 50 diagram/month is looks like a better option compared to the free but it's still a paid option.
It is cumbersome for me to start another paid service let alone another risk of trust I am putting myself in.
Make it free option 15 diagram/month and let people try your site fully so that who uses it that 15 diagram can switch to paid option.
Other than that, great implementation.