Against some [censored] who has a knife or thinks that he's Mr Ninja-san they are reasonably effective.
A couple of points to remember:
1) Confine your blows to his extremities. That means his arms and legs. NOT HIS HEAD! Your trying to discourage him, not kill him.
2)...snip
When facing someone with a knife, the issue has already escalated to a deadly force situation and I'm going to take whatever target is presented.
Truthfully I have an ASP but almost
never carry it. Choices are usually whether to employ OC or a pistol.