Speaking out of curiosity, can you name some companies that provide NDA-laden USB-serial bridges? I'm painfully aware that it's hard to even know such products exist, especially when your production volume barely runs into hundreds or thousands and you're not established in the industry... and from my limited interactions with even the smaller players like SIMCom or SiRF, it takes an NDA just to talk to someone who can get you to sign a second NDA so you can see datasheets. Even if you have tons of money, giving it to such company in return for their product can be a challenge.