I find this amazing piece of complex software to be an excellent aid to my driving. In no way is it infallible and therefore should never be used over your own driving skills, as I am sure a magistrate would agree, but it may just save one speeding through lack of concentration, as I am sure we all suffer from time to time. I have used it for the last 9,000 miles.
It does have a few quirks:
I drive on one stretch of road where tracked military are limited to 20 in an otherwise 40 zone. It thinks I am driving a tank.
Another stretch of 30 zone road runs parallel with a railway line and it is happy that I try to keep up with the train by reading the 60 sign at the side of the railway.
I also find that low sunshine and sometimes rain effect the ability to read the signs.
Also, once you've driven long enough within one limit that the car's got bored with showing the sign and starts showing "---", the system will no longer keep you within the speed limit.
I've never seen this issue but if I know that I am going to be within a 30 for a while, then I will switch to the manual limiter mainly for the following reason:
There are two annoying features that I have found. Firstly when you indicate to turn (down a side road at 90 degrees for example), the system will cancel. This only happens if you indicate and turn so is obviously intentional. I cant see the logic in this.
And secondly, when you stop the engine and restart it (maybe at the end of a journey), it does not remember the limit that you were last in. Therefore if you start your journey in a 30, which I suspect is in the majority of cases, then it will not be functional until you pass a speed limit sign.
The only other sign mine has ever identified is a "no overtaking" sign. I would be interested to know what other peoples cars have recognised.
To sum up, I think it is quite amazing that it works at all, given the complex task it is expected to do and it is one of those features that you will love or hate and must make an individual choice on whether to use it or not. But as with other gadgets that have been discussed on these forums. You are the driver and it is up to you to stay within the law.