As far as I know, there's no way to detect this in game (or in any mods) since this is entirely client side. The entire blocking process is handled client side. Tonight or tomorrow I will go on cRPG and use it several hours+ and we'll see if I get banned. (I don't really play cRPG and don't care, have multiple Warband keys so don't care about that either)
That said, I can't be 100% sure on that. And if somebody watches you and determines you're using it, you can get caught that way. My advice is to NOT just hold down defend, it's easy to tell that you're using it if they start feinting like crazy (since you'll react exactly every time). Just right click when they're swinging and you'll be fine.
Use at your own risk, of course.
I like this quote from that thread on cRPG btw:
"Should actually hang the guys coding stuff like this.
And their families, afterwards ofc, after they watched their own genetical waste dying."
lol, priceless