I've been using it over the last month and found it tough going - the documentation is light, tech. support take a while to get back regarding any issues and things don't always work consistently. We use sip voip and this isn't supported well nor is outbound dialling very sophisticated - it is basic autodialling with no predicitive dialling ability.
The pbx side however is quite good and stable, we're runnign around a dozen extensions and external lines and that was easy to setup and configure.