In the frontend of your site EasyLayouts acts as a dynamically created template override - it involves a couple of very fast database queries from a small database table and the logic for rendering the page will add almost no overhead to a page load.
With EasyLayouts you can continue to use Joomla caching and any JS/CSS optimisation tools you have running on your site.
In short - EasyLayouts will have little or no measurable impact on your site's performance.
Try it and see!