Hi guys. SP PB 4 looks impressive. Great job!
My feedback:
The editor is too narrow. It would be great if it could be increased and would be full mode. In addition, it seems to me that the fixed position would be better for this.
Same for HTML editor.
When you hover on the section there is no highlighting the upper border, which is not very convenient.
When adding a new section, there are no custom columns settings. Now it is not possible to create multi linear structures.
Also, these settings are generally not in the already placed section.
The windows are not adapted to the height of the monitor. Now you can work comfortably only on a large monitor. On a small monitor it will be abroad visibility.
Positioning settings are absolutely not suitable for use. Instead, we have to use CSS.
Must be top, right, bottom, left settings, but not X Y.

Also, there are a number of bugs. But I think this is the cost of alpha version and there is no point in listed now.