Ferrari aftermarket tuning specialists

Ferrari aftermarket tuning specialists are rare, but there are some great companies out there that specialize in exotic cars and have all sorts of engine upgrades, ECU's, suspension kits and so forth for Ferrari's like Koenig, Novitec, Hamann. I've gotten many engine upgrades from them. Check them out at

http://www.koenig-specials.com
http://www.novitecrosso.com
http://www.hamann-motorsport.de

Have any of you ever done business with the companies above and purchased any of their products? I'd like to know what you thought of their service and quality of products.