It only lets you preview for desktop, not mobile or smaller screens. Careful using it. It does not actually edit your files. Uses script to pull changes css from them and its more resources and slower loading. If you no longer need to edit your work, too bad. Remove it and everything you did is gone without warning. You must keep paying forever. Support is poor, perhaps different time zone but for this an other apps of theirs, they look great but good luck talking to anyone. Nice offerings but there are strings attached.
The app got too much bugs. Did all the modifications and saved it, but it became useless. The changes will revert back to its original form after a few hours.
I used to adjust some elements of the site. It looked fine on desktop but totally jumbled the mobile aspects. The app doesn't let you see the effects in both views while editing. Also had an issue with elements in the editor not showing up on the site after being saved and it did not work in some aspects of the site. Its quite buggy. I was told that I could uninstall the app and all elements would return to the original look and I would lose the webyze theme editor changes. This did not happen and now have to find solutions to this debacle. I am very disappointed in the app and that shopify allows buggy apps on their app store.