I think that one of the following behaviours could be implemented into the quick Outline Pen tool for more comfort and ability to quickly preview outline width and change decision on the fly:
1) The outline width of a selected object updates immediately when the cursor is hovered over a certain value (e.g. 2 pt), without even clicking on it; unless it's finally clicked, it goes back to its original width when the cursor goes off the Outline Pen toolbar.
2) The expanded Outline Pen toolbar doesn't close after clicking a width, only after the cursor goes off the Outline Pen toolbar. This way, after picking a width we wouldn't have to make any extra clicks to reopen the toolbar in case we want to change our decision.
I believe such a little change would benefit in user productivity.