Q: Can I place Menu items everywhere?
A: You can place menu items in all places except for two places; 1. Under the sub-menu of other add-ons (more info further down) and 2. As a new menu on the top-level structure (File, Edit, View, ..., Help)
Q: You say that you can't add new menus under other add-ons. It seems to work for me (sometimes). What is the reason?
A: The reason we say it is not possible is that it is dependant on different startup add-on speeds. When you place a new menu-item it needs to happen under what is called a parent menu item. During startup of SAP Business One (and it's add-ons), if the Add-on that has this parent menu-item is slower to start that B1UP, we can't add the menu-item as the other add-on has not created its menu-structure. So while you can set up a menu item and it seems to work while configuring we can't guarantee this for next startup and for that reason we officially can't say we support adding new menus under existing Add-on menus.
Q: I've added an Image to my new menu item but it does not show in the Main Menu. Why?
A: This is because SAP only shows images is when you create a new Main Menu entry (aka on the same level as Administration, Sales A/R etc). In all other scenarios the images are not shown (but they are shown if you look at them via the top menu).