Corgi Vatsaver

I've been given a letter which has been sent to my client who's a plumber; it's from CorgiVatSaver claiming that they can make substantail VAT savings on  boiler installation for a percentage of the savings made.

As far as I'm aware you can only charge VAT at the reduced rate on the installation of electronic timers, theomostats, mechanical or electronic valves. When fitting a heating system I understand that the fitting of these engery efficient materials are an incidental part of the whole installation and would therefore be charged at the standard rate of VAT.

I have found some comments on the internet regarding the Vat optimiser which seems to have been offered by the same people and understand from these comments that they are trying to seperate the installation into  standard rated supplies and the reduced rated supplies to claim the reduced rate VAT, but this is being desputed by HMRC and can put plumbers at risk of having to pay the VAT back.

Has anyone out there had any dealings with this? I would appreciate any comments.

Thank you