With the scope of the information that I can collect,and taking in consideration the paid accounts, and API usage, I could say around 5k? To be honest I don't know exactly how many installations are out there, I don't ping.
Imo the number of installs is data just about the surface. Is the base number to define your size, but it has a completely different mean here, it just miss the number of actual endusers. The actual people using it for sharing their photos is beyond my knowledge 😱
What I'm most looking forward is to create Chevereto derivates. It will be great for me to study the versatility of the thing in real projects.
Nowadays I've been using it in documentation and it was great to get the job done quickly. I believe it took me less than a week to do everything from zero for both projects.