Friends in the engine development departments with Detroit auto companies. Both have heard of every additive on the market.
They both recommend the same additives that their companies recommend - NONE! They simply have never been proven to be needed.
We are in the same BMW motorcycle club. Nobody uses such additives in their motorcycles. These engines thrive at 6,000 - 8,000 rpm at cruising speed all day, can produce 100 hp/liter or better and will go 200,000 miles without a rebuild given regular service.
Long-winded way to say I wouldn't recommend it either.