Sorry, I can't comment as I haven't had my mits on one yet. I would imagine you can use it to downgrade numerous units, but as said, the dual boot would be console-specific...
I think you should be able to Downgrade/dual boot with that PS3, but to make sure you can always check if that PS3 has a base firmware of 3.55 or less following this (http://www.ps3news.com/forums/ps3-gu...hk-120995.html) guide just to make sure.