$10 for a precision instrument may or may not be a deal. If it let's you down when you're counting on it what could the damages cost you? Say you torque some rod bolts and the $10 wrench gets it wrong.
Not that high quality often expensive tools never fail, but the odds of continued sucess are better.
I work with a lot of precision measuring tools and even though a cheap one might work, to me it is usually not worth the trouble and worry of second guessing. Spend a little more and enjoy using the tool instead of waiting for it to fail.
