I purchased one of these after hearing of horror stories of the BMW dipstick snapping off in the dipstick tube allowing a piece of metal to potentially damage your engine, £66 seemed a good amount of money for the piece of mind.
However after taking my car to a reputable tuner pre health check and dyno run the oil level was checked with said devise and i was asked how i knew if the level was correct, i explained their was 4 notch marks so i assumed that they were quarter marks. The oil on my dipstick was at the top notch giving me piece of mind all was ok.
The tuner then used a genuine BMW dipstick and to my horror the dipstick was bone dry!!!
almost 2lts of oil was added allowing the dipstick to at least have enough oil to ensure the tuner to complete the health check and 3 dyno runs.
If you are using one of these i highly recommend you replace it ASAP.