I know they offer several designs chambered and non chambered. Although, I have only heard a 3.2 with a cat bypass with a single in single out chambered Spintech, it sounded very similar to a chambered Flowmaster. Being that the Spintechs do not have such a loyal following as other name brands, they seem to be quite a bit more expensive. That being said, I have seen limited model numbers listed on ebay for reasonable prices.
Here are a few posts.
http://forums.pelicanparts.com/porsche-911-technical-forum/100051-its-not-light-loud-enough-yet.html
http://forums.pelicanparts.com/porsche-911-technical-forum/134755-anyone-know-anything-about-these-mufflers.html
On a side note, I have been happy with Magnaflow and if I remember correctly so have a few other Pelicans.
Being that I like to tinker, I have recently purchased a Borla 400024 multi-core that I would like to experiment with. On paper, this particular muffler seems to offer the best of both worlds in regards to straight through flow and a significant reduction in noise when compared to other straight through designs. We'll soon see when I have the opportunity to test it out. Here is a pic. for reference.
Regards,
John