I do not see a difference, in both cases there are two clicks.
Open the dialog = Open the menu, go to View > Go To > Open Directory/Bookmark, then move the mouse to the bookmark I want, then click.
Strictly speaking this is two clicks, but in between there is a lot more mouse movement than would be with a toolbar dropdown. You can do a stopwatch test :)
Or you can read about Fitts' law for mouse movement.
Or explain to me what I have done wrong..
I could also do Ctrl-O + click the item, but I usually need two hands for Ctrl-O and then need to move one hand to the mouse..
Or I try to do it all by keyboard: Ctrl-O, then tab my way through that dialog, then enter - I tried that, but was not happy with it.
I think a dropdown (or a bookmarks menu in the menu bar) would be faster, feel more natural, and be more obvious for new users.
Local > Add to bookmarks
View > Go To > Open Directory/Bookmark
None of that feels like "manage bookmarks". It's mostly a matter of labeling, I think..
Do you want to start session in certain directory? Or cause existing instance of WinSCP to switch to different directory?
In this case I would want the existing instance to switch location. But, really, that's only for this one use case.
I don't insist on this commandline thing, I was just thinking how one could get a keyboard-only solution.
A very easy alternative would be to set the focus on the list of bookmarks, when you open the dialog with Ctrl-O. Right now the focus is on the "Remote directory" text field, which doesn't help much if you want to quickly jump to a bookmark.
It's all micro-optimization, but that's the entire point of bookmarks, isn't it?