Speed Limit Display? I think it is very useful indeed.
In the HUD it is close to your line of sight and therefore a constant reminder to keep close to the speed limit.
I find it pretty accurate and therefore tend to mostly rely on what it is telling me.
It is quite surprising how many B class roads in SE England can be quite wide or remote from houses yet still have a 30 or 40 mph limit.
Unless one is always belting up and down motorways, I say the SLD is very useful and would for sure have it again on my next motor!
The HUD display? Quite superb! A must!