1Dot Low-end server is usually VPS with 1 VCPU. If such server is able to handle 5 RPS, then 10 opened cards will drain all server resources. In the same scenario websocket-based solution has almost no overhead. Advertising your extension as lightweight is just not true. It is simple to install, but that is it - in any real use case it is probably better to use Pusher (even for large forum it should be cheaper than paying for server that is able to handle additional overhead from this extension).
