As a GUI designer, I find the visualizations hinder more than they help. Consider this GUI where I am attempting to place a TextLabel at a specific position so it lines up with a graduation next to this dial:
You can barely see the tick mark above the large yellow boxes, and the textbox itself is completely covered. The issues with the visualizations are the same as with drawing Constraints over parts. It blocks the view and makes it a game of Select, Move, Deselect, Select, Move, Deselect in order to try to find where the GUI needs to go.
dragging GUI elements has limited precision, so to add to the time consumption I have to write a text in a valid UDim2 format to change the position of the GUI.
As a suggestion, there is plenty of room here to add properties for the GUI visualization: