To throw in my two pennies worth of my box experience so far.
When buying, Andrews suggested I go on a spin at 1+1, 3+1 and 2+1. Found 1+1 aggressive, 3+1 refined and 2+1 the one that seemed right.
Perversely (?), have been driving so far on 3+1.Wanting to give each setting a good outing over time, before coming to any final preference conclusion. MPG is interesting. I had been getting 49 to 50 mpg consistently - real figures on a tank fill and not screen display figures. With the box in, the screen was showing a clear improvement - up to 10% on some regular runs I do. Tank fills show about 47 mpg, which is more in line with what I would expect. I had read somewhere that the box can fool the screen display, but I don't pretend to understand why.
Downside so far? The very occasional power loss blip (I wouldn't call it judder) while driving. Can't pinpoint what I am doing when this happens. I am certainly not overtaking or something like that, as never any
problem when 'using' the box. Have tried not to change things, so could be the need to move from standard supermarket diesel?
Plus side? Well, only to say that I cannot imagine driving without it.
Will shortly be changing to 1+1 for a while. Further comments to come anon.