If you want agreed value (in case of total loss) then you will need an approved valuation, well worth having otherwise your insurer is allowed to reduce to 'market value'
It's sort of a bit like paying Gap Insurance on a tintop
There is no real "market value for a Morgan as they are all different, when I got T-boned last year I was with Admiral no agreed value. Their assessor asked Melvyn what the cars value was and used that figure to approve very expensive repairs.
