Either way is good. If you email your suggestions and ideas directly to the support site, the developer will be able to more easily discuss your ideas. Posting them here, might get a bigger audience and spark new ideas in other readers.
If there are things you don’t like about the way myCardLists operates, please send an email to the developer. The same applies to things you find confusing about the app. Also, if you think there is something that could be added to the app’s website to explain how to use the app, again let the developer know by emailing the support site.