Can he guarantee that? Is he willing to replace anything on your car if it blows? Is he responsible if something goes wrong? Just because hes an engineer for 20 years doesnt mean he knows shit about you or your car.
Yes numerous people have put additives in their car before, and numerous people have burked their engines by it running too hot / out of tune / wrong mixtures.
People recommend it to clear carbon, and clean the fuel system, but not recommended for long runs on it. If u get your car tuned to suit then go on a long trip, are u gunna have a few litres of alcohol in the boot to top the tank off with?
No need for agro mate, ive seen the results of people doing it, and yes motors have died. Your valves dont like excessive heat and can melt and drop into the bore, which HAS happened to a board members here.
I guess i wont bother in the future...fyi go put some toluene (recommended fuel additive) in a plastic cup and tell me it wont have any effect on rubber hoses.