Fed says it must be registered, but state law says it doesn't have to be registered. Does that correctly sum it up?
There is a difference between not requiring registration and saying you don't have to register it. My understanding is that while there is no state requirement to register it, the state law does not exempt you from having to register it with the Feds.
I am certain the Feds expect you to register it (and do so before manufacture), they have prosecuted people for not registering units that didn't even work! IF you make something that you intend to use to reduce the report of a firearm, without getting Fed approval beforehand, you are in violation of Fed law. That's my understanding of it. I could be in error, but I don't think so.