Saw that your screener filtering is instant. Do you have everything loaded to the client side? If you want some feedback, I think the filter slider for the active rule could use a bit of a redesign. The magenta color is too vibrant for me and the actual bar itself is barely visible (could use more contrast against page background).
For data providers, have you looked at EODHD? They are a bit more expensive compared to FMP but the data is a lot higher quality from what I've seen and they have 24/7 live chat support. I don't know if it would fit your budget but could be worth to ask their support. Disclaimer: I build something similar in this space and I'm currently trying to migrate from FMP to EODHD.
Always fun to see others build tools like this. Would love to chat more on discord if you are up for it. Just followed you on twitter so we could go from there. glhf