Well, I would have "discovered" them earlier if the tooltip was more clear about what they do. The catch is that they only give first strike on the first of the two attacks, and you need the dodge setup to get a better cydstep out of them.
The effort required is just about right for them being balanced slightly above the curve, and they make quite good preps for hard hitters and anyone trying to avoid debuffs. They also make a great way to deal with glass cannon bosses, so I'm deffinitely using them on gold acquisition tinker runs, and getting 2 "free" hits in when you have enough damage is quite the deal - I've discovered them against the final boss in Dragon isles. The old genie boss, any major berserking bosses, and some of the guys in the demonic libraby also make good targets I guess.
Come to think of it, the only place one pair of them isn't a good idea is against damage sponges, and since you can prep them, you don't even have to "waste" a HP potion on them, or need to find TT.
I almost got pwned by Shifty Brickwork!