Yeh, at boot up hold 'x' or 'y' or nothing to boot any 1 of 3 OS's in any order you have set up to... scds-1, dstt or Y's (Yasu) menu.... and of course you can run the Sakura menu too, as can any cart, though you can't boot commercial games from Sakura.
You can also load from 1 OS to another, this gives you instant accessabilty to basically every function there is available for ds flashcarts.