To be honest, I am personally not completely convinced too which is the best approach. But I guess the most popular solution now is to use a separate element to just trigger the sub menu – e.g. a +/- icon button – and (also based on user feedback) I have actually now decided to switch to this behavior as a default in the next version. Though I will probably not do this for the Bootstrap add-on since I prefer to keep Bootstrap’s default behavior as this is just what most of its users would expect.
As for Bootstrap’s solution, it obviously has one disadvantage and it is that it does not allow activating the link of the parent item if it has an actual href set (unless the user long taps and activates the link via the browser context menu).