Complete and utter bargain if you have mechanical knowledge
Utter bargain at £29 as this was selling at £199 when bought through bike shops. The only caveat is that you have to install it yourself and then check calibration using the AVIO Installer app.
It needs bonding to an existing Shimano left side crank arm using epoxy glue and clamping for 24 hours.
Once bonded re-install the crank arm to your bike and put a battery in and you are ready to go.
Mine didn't need calibrating as the factory calibration was still within parameters. There is an excellent YouTube video made by AVIO about troubleshooting which shows all this.
Unfortunately AVIO are no longer trading so there is no warranty but one I had fitted to a Dura Ace crank arm 4 years ago still works perfectly.
Verified purchase: YesCondition: New