The short answer: absolutely not.
Recart's code loads on websites asynchronously, so it will never block or slow down other parts of your site that are actively downloading. While web page analysis tools may show that Recart loads later than other resources, this is entirely intentional.
Basically, the page load speed is not impacted by having Recart installed because Recart's assets are not placed on the critical render path for your site and any images and stylesheets used are delivered via a global CDN to minimize load time.
Need more information? Please reach out to us at support@recart.com.