pay 25% for something he wont notice with the possibility of damp sounds good?
Well we never got damp as a result, and although we didnt notice a difference, it supposedly helps retain heat.
IE. when we turned the central heating off, it supposedly kept the heat in longer then without it.
I never noticed it, nor did my mum, but its not something you really think about. It must work as they are filling the cavity in the walls (provided you house has them) with insulation.
We already had two sets of loft insulation, the original one from when the house was built and they put a second layer in as standard when they did the central heating.
Id be very surprised if your house didnt already have one or two layers of loft insulation.