Oops, my bad. I didn't see the detail on the right page about the premium plan. Quite expensive if you don't trade regularly for $6 a month imo, but there is a discount right now so you can buy it for around $4. Yeah, it definitely has a good UI, you can use it as your inspiration.

I search further and found another website that can be your inspiration/competitor, it needs registration but it is free according to their faq (https://altfins.com/alerts/notifications). Looks like it supports RSI too. It has an IOS app, however, based on the feedback from the users it is terrible. It needs some rework so you have to use the website if you don't want any problems.