Hi,
Thanks for the interest in Pro. We do not have a demo, but we do offer a 30 day refund period so you could get it and it does not work you can ask for a refund.
A first step for compatibility is to try the core version of the Events Calendar found for free on WordPress.org: https://wordpress.org/plugins/the-events-calendar/
If that works most likely Pro will work too as Pro is an Add On for core and uses many of the functions from it.
If you do have issues with core we maybe to help, but please post the WordPress Support Forum for the Events Calendar:
The Events Calendar
If you do purchase Pro and would like some help please post in the Pro forum on theeventscalendar.com. We maybe to help, but many times theme compatibility is beyond what we can support.
Thanks again!