So having read the RRS owners manual I still have one question.

What is the forward alert system and button in Center console all about? Is it necessary for acc cruise to function ? Do you use it much ?

Is the default cruise gap ok for motorway? A roads?

From memory, the forward alert thing is just that - it tells you if you're too close to the vehicle in front in a closing distance situation (i.e., they're slowing down and you aren't). In effect it's the first gen version of today's comprehensive AEB system but without the braking function. It just gives the driver, who is presumably not paying attention, a warning that they need to brake.

Forward alert uses the same sensor as ACC but it doesn't have to be on when using ACC. Indeed, having played with it once, I never used it all in the 125k+ miles I did in my TDV8.

When using ACC, I varied the distance to suit conditions. If traffic is a bit heavier, having a closer distance set reduces the risk of people "diving in" and causing the system to hit the brakes. So being closer is a little safer, ironically. But otherwise I found the default distance ok most of the time. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Thanks for your reply. That’s just what I needed to know