It is dangerous.
I tried it yesterday for the first - and last - time. On the highway, it picked up a speed limit sign that was intended for the side lane, and started reducing my speed fast and unexpectedly.
I love the speed limiter, the dumb version. I think it's a super nice way to avoid accidentally going over the speed limit without having to keep an eye on the speedometer, and therefore off the road.
I would love to use an intelligent speed limiter. But let's face it, there are always cases where those things will fail unexpectedly and dangerously.
That's not even considering voluntary tampering with the road signs. What if I put up a 5km/h sign along the highway. How would the car determine it's bogus?
I wouldn't mind a global limiter that prevents going to unsafe speeds well over the highway speed limits.