Just looked at the website, it basically just plays a message to incoming callers stating whatever style of message you want i.e: "we don't accept cold calls" and instructs any 'friendly' callers to dial 5 to be put through, whereupon your phone rings.
In a nut shell; it doesn't stop anyone calling your number that is capable of pushing 5, so will only guarantee cutting automated calls. And in answer to my previous post, claims not to interfere with BB.