Ametech Engine Restore will help in the short term with certain types of high mileage wear - worn rings, for example, or slightly rattling shells.
This will buy you a few thousand miles whilst you amass the money and parts for a rebuild.
It can also help in the very early stages of piston slap onset - but again only by delaying the inevitable.
Things it cannot help with include, but are not limited to,
broken valves or springs,
camshaft wear,
slipped liners,
piston skirt damage,
big end knocking,
porous block,
blown gaskets
Piles or HIV
A solution to the Palestinian issue.
However on my old 180000-mile V6 2.8 Capri, the oil pressure light was flickering on and off at tickover and I knew the rings were going - a litre of this stuff and some 20/50 and a new filter restored healthy oil pressure and I ran the car without problems for another 5000 miles over two years (I was a student and not too wealthy).
So, it can be useful as a short-term fix