Be sure to ask him about the 9Octane or 9Osprey as an alternative to the AAC product. AAC's customer service is so poorly regarded you might be well served to consider alternatives.
I bought a Specwar 5.56 from silencershop.com, waiting for ATF approval. From some of the prices Dustin has posted lately, I regret not purchasing through him. I would have saved the effort of trying to find a local dealer for a NFA transfer, and his posted price was very competitive to what I paid.