[Moderator note: Please don't type normal words "LIKE THIS". That's considered as shouting.]
I am checking out your Demo site.
Using the latest Firefox or Safari browser in a MacPro I consistently find that merely selecting to see another month and then another month it takes 12 to 15 SECONDS to appear!
I tried all the different Demo calendars and same action. Painfully slow response to just pull up the barebones numbers that make up the next month's grid.
I am used to seeing other booking and availability calendars from simple to complex whether Joomla, WordPress, or PHP/MySQL based sites simply load the next month in milliseconds to one second.
I would figure that your Demo site would be primed for maximum response. So, something is WRONG that the simplest calendars possible are unbearably slow to load one month to the next.
I stopped considering a purchase once this kept happening.