Hi Bartosz,
Thanks for looking into our plugins!
I understand your concern about making that investment. Fortunately, we offer a full refund within 30 days of purchase if you are not satisfied with the plugin. This way, you have a chance to try it out, and if it doesn’t meet need your needs, we are happy to refund your money.
To answer your question, this site (theeventscalendar.com) is the only official site to buy Events Calendar Pro from. Any other source would not be an authorized distributor.
Again, thanks for checking us out, and please let me know if I can help with anything else!