It's a plugin, but it acts like it's own "download" to the user, so whoever has Tapatalk on their phone or tablet needs to have it installed on their phone, on the server side, it just outputs the plugin to a device like a sync. So, every time Tapatalk sends info to a device it's only using 5% of server power.
It only slows down when there's like 1,000 users using Tapatalk to access your site.