We've had these and other 'finger probes'. Whilst they were in service their accuarcy was good and the build quality was as good as could be expected for a small item.
The 'trouble' is their size - they're easily dropped and they go 'walkies'.
We didn't get to the chance to worry about calibration/ppm/reliability as they've all disappeared - nicked, lost or gone in the laundry.
They were purchased against our better judgement - we knew that they'd 'walk'...obviously.
Cheers
Mark
