The bright side is that in most cases it doesn't hurt to run it through... except for maybe your wallet.
Once knew a guy who bought a product "guaranteed to make worn engines like new". He was surprised when the results didn't match expectations on a 200k+ mile slant six... as a good Christian he believed everything he read was true.
If carbon and oil soot are built up in the combustion chamber causing poor performance, some of these magic cures can actually do a little cleaning internally. Down side is if that build up is keeping a little compression going. If cleaned out, so goes compression....sort of a lose, win, then lose again situation.
I have to chuckle at the "Mechanic in a bottle" label, someone's idea of comedy I suppose.
Worth a try, who knows maybe will improve a little. If not, you are no farther behind than you were.
When I first started reading this thread, I thought back to a little Datsun truck I had years and years ago, where its engine was starting to get pretty loose at about 220,000 miles. I thought, 'what the heck, I can't hurt it', and did a couple oil changes with Arco Graphite. Remember that crazy stuff...?
Anyway, after a while, it stopped the oil use completely, and the oil light would go out on the first turn of the starter. Sold it soon after, confessed to the guy that it was going to need a rebuild REAL soon, but he desperately wanted cheap and solid transportation. Saw it running around for about another year.