Worked with the on-premise version, and I'd avoid it like the plague. Badly designed mix of XML and old-school Java, if it wasn't for political reasons we would have kicked it out.
XML/Java is very much it's ancestry. Back in the day, it competed eye-to-eye with ServiceMix and Camel. Both of those have remained firm Apache products. Mule ESB was heavily commercialised, for better or worse.