Clean and stable. Does what it says.
An option so see the different break point stylings – so that you could edit them separately.
Maybe some more Sketch- / XD- / Figma-like features. Or what about an built-in code editor? Or something similar like a "visual code editor" like Webflow.
Btw, watch out, if Webflow releases a "code-import" feature, you could get a lot of troubles :) JFYIDaniel Prace has used this product for one day.