We believe there are more important elements of the web page that should load first. Usually, a customer needs at least a couple of seconds to look over the page and decide to view the size chart.
If you still want to load the app faster you can add this to your theme.liquid file after
{% render 'sizechartsrelentless' %}<script src="https://size-charts-relentless.herokuapp.com/js/size-charts-relentless.js"></script>So it looks like the below.
{% render 'sizechartsrelentless' %}
<script src="https://size-charts-relentless.herokuapp.com/js/size-charts-relentless.js"></script>