Can anyone tell me if its worth have a kind of graphite beads put into the wall cavity of my home.
The house was built in about 2002 and has no insulation in the walls at the moment but I keep getting people coming round insisting I should have it done and that its free.
I just don't know what to do, is there a real benefit or not or could this even devalue the home??

+1 It's unlikely a house built in 2002 has no insulation.

You do need to be careful before filling just any old cavity wall. In some cases filling a cavity wall can cause moisture/water to cross the cavity causing damp on the inner leaf. That would be a big problem if the inner is a timber frame. The outer leaf of bricks can be quite porous.

Having said that, I believe the graphite coated bead system is less prone to this problem than other systems.

I would recommend getting someone independent like a surveyor (rather than an insulation salesman) to look at the house construction first.