speed kills
If I want a gadget to make sure I do not excced any speed limit on any road - I set my cruisie control and what we call our "useful gadget" (RA/b2) - yup - use one in my private car and see no problem with using one wisely

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Both gadgets make an audible warning when I am at or just marginally increasing limit and I can adjust accordingly.
We have means at disposal if we so need them. We do not need a limiter which could be deadly on motorways in Europe - especially parts of Germany - as Peter says.
I do drive on continent on my jollies - and I observe their rules whilst I am there. A UK car limited to 11.25 mph
below their dry condition speed limit on a two lane motorway could be very dangerous - especially when you take slow moving articulateds into the equation and you have pulled into outer lane to overtake and Turbo Rolf storms up at more than twice your speed whilst you are overtaking...
Fors and against in any technology and I would rather see a human being retain skills and accept reposnibility for themselves instead of relying on some gadget to do their thinking for them
Because as Gatsobait so rightly points out - leaves them free to use inappropriate speed in built up area or in poor weather conditions.
More reliant on gadgets you become - less you think for yourself and that, my friend, is very dangerous..
Said it before - I will repeat - we need to improve driver training and testing.
We can do that via police, adverts, governmenent policies, and training incentives. Focusing on one area of driving standards is not improving the whole.