All engine flushes work pretty good.

Directions on the can will tell you what to do. But you really only need it if you don't change your oil enough. If you change it all the time there isn't any sludge left and you don't need to

I just put liqui moly engine flush through my 95 Miata last week.  I think the previous owner generally maintained it ok, but it was sitting behind a barn for 7 years before I bought it.  I changed the oil with cheap oil from Walmart, ran it for a few hours, added the flush, and changed the oil again.  The oil coming out was black similar to 10,000 mile oil.  So it certainly pulled out a lot of crud.  (Too soon to tell if it will make much real difference, but it idles smoothly now.)

To me, that’s probably the best case for an engine flush.  An old engine that needs some TLC.  The concern is more for newer engines with complex VVT systems and such.  The theoretical risk is that they have very small oil channels that could be blocked by all the gunk the flush loosens up.  So if you have a newer car, the risk-reward might not be favorable.