NO organometallic compound is GOOD for engines.
The nonsense about safety and EPA approval is hogwash -- EPA specifically prohibits the use of lead in fuels for sale, and does not, to the best of my knowledge, approve or dissaprove of fuel additives for consumer use.
The idiocy about lead being "good" for engine parts is hogwash too -- this was propaganda bandied about by the American automobile companies to avoid putting inserted valve seats in cast iron heads, nothing more. The theory was that a layer of lead oxide on the valve and valve seat would "wear itself" as a permanent self-ablative coating rather than the valve or seat.
That turned out to be wistful thinking at best. Lead oxide, like all metal oxides, is considerably harder than any metal found in an automobile engine, and will grind away constantly. The oxidation of tetraethyl lead will produce microscopically fine, breathable, lead oxide dust -- this blows out the tailpipe as well a fusing to things like exhaust valves and spark plugs. It also gets into the oil, and very fine particles will circulate right through the filter, so they constantly "polish" the bearings, cylinder wall, and valve train.
I rememember lead fouling -- under load, the lead oxide melts and shorts out the plugs. Happened all the time to "gear heads" who just had to have 13:1 pistons and over-advanced timing.
Lead will also instantly poison a catalytic converter and render it totally ineffective. This is not good -- I also remember the stench of semiburned hydrocarbons in LA and Germany before all cars had cats. Not very nice, bad enough to make your eyes (and lungs) burn.
Any modern engine will run fine on commercial lead-free premium, you aren't going to get any improvement by adding lead to the fuel.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!