I think they are relatively rare. In my opinion, they should only be used when it is clear what will be encountered and that the no-knock is better than the alternative. Unfortunately, they are often allowed when the police don't know what they will encounter so they think a no-knock and the element of surprise will be better.
As a law-abiding citizen, I know for sure there is absolutely no reason why a no-knock would be served at my home. As such, I have no choice but to defend myself and my family from anyone that kicks my door in at night - I don't care if the guy's flashing a badge, has SWAT on his jacket, says he's a cop, and is smiling and wearing a CTR ring, if I feel threatened I will neutralize that threat in my home unless I'm 100% positive that it is a cop.
As a law-abiding citizen, I know for sure there is absolutely no reason why a no-knock would be served at my home. As such, I have no choice but to defend myself and my family from anyone that kicks my door in at night - I don't care if the guy's flashing a badge, has SWAT on his jacket, says he's a cop, and is smiling and wearing a CTR ring, if I feel threatened I will neutralize that threat in my home unless I'm 100% positive that it is a cop.