if its attached perm to the preban barrel since it doesnt have holes a flash supressor does

I'm not sure what you are asking.

Huh???

I think what he is asking is would perm. attaching that device, whatever it is, to a preban barrel make it okay for use on a postban lower receiver.  

Ask yourself these questions to determine whether or not what you want to do is legal:  

1. Is that a legal postban faux suppressor?  In other words has the BATF deamed it legal for use on postban compliant weapons?  Remember a real sound suppressor is also classified as a flash suppressor so there is no way to attach that legally to a postban lower.

2. Assuming that it has been BATF approved the next question is; does the preban barrel have a bayonet lug?  If yes you will need to hack it off or somehow render it unable to attach a bayonet.  If no then don't worry about it.  Best way is to order it without the bayo lug.

3. If you are using a shorter than 16" barrel will that device, assuming it's legal to attach, bring your shorter than 16" barrel to the legal 16" length when perm. attached?

If  your answers are yes, no and yes then I would see no reason why it wouldn't be legal to mate to a postban lower.

well i dont have a bayonet lug its a gas block

and i been told my flashhider/muzzle brake is illegal on my upper, (it would sure make a flash if i shot it)  but i think it would be cool to add a fauz silencer as it would be a muzzle break since its not a silencer

As long as the ATF has deemed that device as a thread protector/faux silencer/extra weight at the end of the barrel and is permanently attached you will have no issues to worry about.