So go ahead - have a play. Note that it is a proof-of-concept toy not a complete tool so please let me know what you think.
You may notice some strange results when you test your website. Many websites have rotating carousels or cookie / advert banners which push all of the page content down, this causes the heatmap to reflect potentially poor results even though content has been rendered earlier. My opinion on this is that shifting the page down for a cookie / advert banner is bad for user experience. So is using a rotating carousel.