i'm an owner of the effeto mariposa wrench, so full disclosure there. i paid retail for mine. it was quite a bit of money, but it offered a nice package (particularly the size, which is an issue for me traveling to races quite a bit).

anyway, what i have seen over the years is that many people do not understand how to properly use a torque wrench, or to properly set the torque for something like a stem's faceplate. i have seen many people blame the equipment when the problem is poor technique.

i read both glowing positive reviews and very negative reviews with the same skepticism. as an example with the negative reviews on slow twitch...
1) that site has lots of people who tend to have quite a bit of money for bike parts and comparatively not as much experience wrenching.
2) with the premium pricing of the mariposa, perhaps it attracts a customer (drawn to the 'high price is best' mode of thinking) that may also have less experience working on their bike. it also may spawn the "it cost more than others so it must just automatically work without knowing how to operate it" mentality.

in that negative slowtwitch post, is it really possible that someone needs a torque wrench to set a cable fixing bolt? that makes me skeptical right there. also, they made it all the way to 10Nm before realizing something was wrong? doesn't take an amazing mechanic to know that there is a big difference in feel from 5 to 10.

in the instructions, effeto say to (and my practice is to) set the torque low, something like 1-2Nm, to "warm up" the wrench. had the user done this he could have determined if there was a problem before destroying a part.

one has to be pretty ham-handed to make some of those mistakes. it's not like he wanted to set it to 5Nm and the part broke at 5.25Nm.

also, we don't know if this guy stores his wrench long-term dialed up to 10, 12Nm, which would affect the long-term calibration. he may also not use short stroke that would trip the wrench.

i'm going with user error on this one.

it's a quality wrench that serves a purpose. it may not be for everyone. it, like every other torque wrench, is not foolproof.

bike parts are generally not NASA-grade projects. it could be that NASA abandoned mechanical torque wrenches (if true) for reasons valid to their work, where a difference of 1Nm could be life or death at Mach 1 speeds.

if one resets the mariposa wrench, stores it properly, and reads the instructions (obviously, all take a bit of care), it is fine. it's not a normal wrench and shouldn't be treated as such. to blame parts breaking on any wrench is dumb.