ok fer wheel nuts , not fer heads ! the more yer use them the weaker the springs get , thus a poor reading / settings ! a goodun is round £40
The trick is not to use them as a general purpose ratchet or breaker bar, but ONLY to set the final torque on a critical fastener after doing it up near with an appropriate wrench.
Also, to ensure you Zero the setting scale on the torque wrench after use, so that the spring isn't held constantly in tension.
Girtie was playing with my 'old' torque wrench last week, cheap £10 thing of unknown make I've had for twenty or more years, and is well battered and abused, and most often has an old jacking handle shoved up it's handle where the setting scale should be to use as a breaker bar....
Like I just warned every-one NOT to use a torque wrench!
But, that's what its used for; I have the Teng to use as a final setting tool.
However, interesting to note; things 2-+ years old and well abused, but kept without the setting scale screwed in, so no tension on the spring; put it on nuts 'set' with the calibrated Teng, and it was within a few pounds of the same torque..... vertainly accurate enough for most jobs, whwere the 'evenness' of torque accross a joint is actually more important than tha actual value.....
For £16, couild be worth having, like my 'old' torque wench; it will 'do' until you can afford something better, and can be 'retired' to being an HD wratchet come breaker bar.