He's lying but luckily I'll take the ADV tank off you for £50 (€75)
OK he's not lying but there is a bit more to it than just fitting, if you have all the ADV internals you are laughing but an ADV tank and standard 1150 internals will see your RID misread, but you do get used to it.
I was keen to get one myself until Fanum and I filled up in Maggor services (he ADV and me vanilla) and I managed to get home in one hit whereas he had to fuel again at Clackets
Should be quite a bit more than a few litres, but get an idea of how much range the ADV tank'll give and use the trip a few times and you'll be sorted. Though if you find all that a cafuffle, my offer still stands
It's no big deal Alex,....... really. the fuel guage drops just the same as usual, but when the reserve light comes on, you've still got around 100 miles.