The Federation of British Historic Vehicle Clubs organised a proper regime of testing lead substitute products under controlled conditions with measurable results. The products that passed the tests for valve seat recession are listed on the FBHVC website:
http://www.fbhvc.co.uk/legislation-and- ... formation/
Some manufacturers of products declined to submit theirs for testing, prefering to cite testimonials from customers to support their claims. Others cited tests done in irrelevant conditions (a diesel truck engine). I believe that Advertising Standards does not recognise customer testimonials as legitimate evidence of a product's efficacy.
So you've got to ask yourself why any manufactuer would not want to have their product officially validated by the FBHVC.