Blind deadbolts are the best possible security you can have on your doors. Let me tell you, as a professional who unlocks things for a living, all keyed locks can be defeated with the right tools and practice. Even those electronic BE365 locks I raved about on the Electronic Keypad page can be picked by an amateur picker. Fortunately petty criminals are usually not inclined to learn a difficult skill to break into a house, they'll usually break something to get in. And once a person decides they are gonna break stuff to get inside, all bets are off! This is a crazy person who doesn't care about making a lot of noise, alerting dog, homeowners, or neighbors. At that point you could have 10 locks on your doors but that won't stop them from breaking a window and climbing through.
But for the really sneaky criminals who invest time and money into their craft of criminality, blind deadbolts are the best. It forces anyone with sheer intent to enter, to make the decision "am I gonna break this window or kick this door right now?".
So there's 2 different kinds of break-ins. The first is the kind that happens while nobody's home, and that sucks, it's scary, and it's so violating. But that's nothing compared to the thought and fear that I'm in bed sleeping and someone is in my house right now! Typically alarm systems only let you know that someone is already inside, while blind deadbolts keep them out in the first place. So these blind deadbolts are primarily for at night when you are sleeping, they make your doors a fortress that nobody can get past without making a lot of noise.