According to mimas, in a thread in the former Linuxvillage forum,
Hi,
> I'll be able to test the openbox-menu alternatives tomorrow - stay tuned!
Even more! Without -p flag,you can add an entry in Openbox menu.xml (<command>openbox-menu -o your_menu.xml your_args...</command>) and manually launch openbox-menu to create a xml file on demand. It could be nice for an old computer with a small amount of memory and power: no lag when displaying the menu, no background task and a menu up-to-date (or at last two clicks away to be up-to-date).
I have never tested, this would be interesting to have a feedback on this tip.