these things have been around since my dad was a boy, and were useful for setting the idle mixture back in them days, and checking things are ok as you blip the throttle.

they can only be used at idle and a bit of blipping while stationary, otherwise they melt.

nowadays your mixture under those conditions is generally controlled by closed loop feedback, so they are no use.

what you want is a thing called an LM-1 wide band lambda reader from innovate motorsports - look it up on the web, there are a few people importing them to UK. cost about 300 notes but you wouldn't want to be caught not owning one.....