In other words, you can't put a save from PowerSavers or Gateway to be messed with. Because in the end you'll have to have the device to re-sign everything like the PowerSaves. Correct?
It only deals with saves/games that it reads from the cartridge, that don't use broken encryption and are supported by the program. You need their device to use the tool, and it doesn't support people with emunand (broken encryption) games.
Cyber Gadget Save Editor allows you to read the save, decrypt it, edit manually/apply codes, encrypt and write the save back to the cart.
Powersaves doesn't do the bolded stuff. Powersaves has codes to choose from, which can't be customized.