3.03 downgrader and leftover files on flash?

a friend has a 3.03 psp and he wants to downgrade, but i think i remember reading somewhere that there are leftover 3.03 files on the flash or something...

are there any problems with the downgrader, or is it "perfect", as in when you downgrade you have a 1.5 psp only, and nothing is wrong with it at all (even if you wont notice it, i want to know anything that would possibly complicate future processes with the system)

even if it is a small problem and theres not much point to say anything about it, i want to know

there may few junks leftover in f0, but as long as it don't bother your psp, let it be called "friend" for now...
In some thread, it is said that we will have remover for these junk files so I guess it won't be really a trouble.

ill tell him to wait for the cleaner thing then, hes scared of this "possible brick" stuff and he doesnt want to do it if there is going to be 0% chance in the future of a complication.