I've been mainly working with the Mobile App editor the past week (just started using Retool).
Today I have been fiddling with the App designer and I noticed that the editor is quite different from the mobile app editor.
I must say I like the App editor more as the layout is better and it has some features that Mobile is lacking or are less easy to access.
there are no debugging options when previewing mobile apps. This makes it more difficult to debug, view console, view states, etc. The App editor does have the debug screen in preview.
no option in mobile to add decription to app and readme documentation
components (to add) are in a different place.
It's not a huge problem, but if you're used to a screen, you'll need to search around a bit.