Here's my experiences:
Krump breaks any hau, though against a vertical unterhau it's a little hairy. It's pretty much a "can't fail" manouvre, hence me calling it "high percentage". Heck, it'll ever break a Zwerch, although it's not as optimal as falling on it with the long edge like Ringeck says to do.
Double Zwerch: Works great from a bind or as a feint. It doesn't matter whether the opponent makes blade contact or not. If there is, you have to try to dominate the bind, and if you can't, cross smash and zwerch to the other side. If there's no blade contact, then zwerch to the other side anyway... no muss, no fuss.
Thust from Pflug: with my new interpretation of Pflug (thanks to Ringeck and the Von Danzig image), the thrust from Pflug is viciously fast, and very hard to see coming when combined with non-telegraphic movement.
Zorn vs. VT. Although the manuals do use Zorn to "break" VT the way that Zwerch does, it's still relatively safe when done with speed. If done properly, it's very hard for the opponent to krump the hands, which is the prime danger. Anything else likey results in a bind, and that's OK. It has the advantage over Zwerch that if the opponent throws a Zorn as well, you'll be reasonably safe as long as the line is closed. Sometimes we've had two opponents in VT both throw a fast Zwerch at the same time, resulting in a double kill. Zorn negates this possibility, though zornhau ort remains a danger.
Schetelhau vs. Alber. This is a no-brainer. A non-telegraphed Scheitelhau is the fastest hau there is. Very hard to react to in time. I've hit people in the hands as they were trying to get to Kron. Nice stuff.
Zucken: it's easy... get a bind, strike around to the other side. It's easy to do, and especially good for beginners to learn.
Duplieren: it's easy to do. Just don't do it without doing your Fuhlen! If the other guy does the same thing, it's a double kill. If you're trying to dominate the bind properly, it's easy to feel coming. However, in the heat of sparring, people often forget and when they just push back mindlessly, this nails them well. It's hard to do on the weak side though. You've gotta move in an almost fasle time from the bind to keep enough pressure so the opponent's blade doesn't slide into your hands.
Nachreissen: Oldest trick int he book after Uberlauffen! Won't work against a canny fencer, and can sometimes result in the "knight's metronome" of strike, hengetort, strike, hengetort that makes that "ting, ting, ting" sound.
But it's great against a fully commited strike that goes down to Wechsel. Don't do it against someone with a significantly larger reach than you... he might hit you in spite of your void.
I found that most of these techniques required very litte in the way of training. It's just very basic swordsmanship, with a few things to do with a hard bind.
In contrast, I've never managed a Mutieren in freeplay.