Startup stock options calculator. Feedback wanted

I'm looking for feedback on the stock options calculator (https://www.cashable.app/) I've built. It's been inspired by my experience of several UK startups. But I wonder if other people find it useful, too. I'm also curious if it's flexible enough to support non-UK startups.

In my experience I've found that tools like Carta are not sufficient. They are good at telling you a number of options you have vested, but they don't give a monetary value. You can't use them for a what-if analysis (what if the valuation goes up or down?). And if you move around between companies it won't give you a valuation of your combined portfolio.

So I appreciate any feedback.