Using your free preview domain at wao.io makes testing your optimization quick and easy. A few clicks and your free preview site _yoursite_.wao.zone is ready to use - no DNS changes, SSL cert transfers etc. required.
There are limitations, because some web services will only work when used on your official domain name (e.g. www.example.com). This is due to the fact, that for security reasons, your browser will block calls from unknown domains (like your preview domain) to certain services.
These services include customized location services by Google Maps (using an API key), licensed webfonts provided by Adobe Typekit or other webfont providers, as well as delivery services like DHL, Hermes, UPS, FEDEX and most payment providers.
So if some parts of your site are not working as usual when testing on a free preview URL, this is not a bug. You will be able to test everything under realistic conditions before going live.