Irrelevant as to what you use, this isn't possible on the DSi as of yet. The DSi will reset to the menu as soon as you pop out the slot-1 card. So no matter what you use, the DSi will exit to it's menu anyway.....(since you must pop out the flashcart and replace it with the game cart anyway)
We must wait until either someone gets homebrew to run from the SD card slot or when someone figures out how to run things in DSi mode from Slot-1 and then after that figure out how to override the DSi's tendency to reset to menu when a slot-1 device is removed. So it will be awhile off before we can do this on the DSi.
So just use your DSLite to do save/rom backups for now.