are they any good?
You only really know if you have to claim.
They are a specialist insurance company, I had my 2.8i Capri insured with them for very little money with agreed £2,500 value and 6,000 miles a year, renewal was £98 !
The point is that they aren't like a normal insurance company working from a script but they will assess each vehicle individually.
They won't develop histrionics if you tell them you have a tank fitted but they seem to operate on a common sense approach.
Refreshing as it's sadly lacking today.
My 02 Ford Ranger was £440 fully comp with the tank declared and covered.