Seafoam is definately a crud cutter..... It's a strong cleaner, and makes a good motor flush. Using it on a high mile crudded up car in the oil is ok for a few hundred miles before a change... I would feel safer with MMO in my oil as a leave-in cleaner.
Seafoam, or Gunk High Mileage Engine flush is a good dump in the crankcase shortly before a drain out. Gunk says DON'T DRIVE IT, just let it idle for 5 Mins, and then dump it all out.
I do my oil changes 1/3 of 10K miles... and every 10K they get a "Bath" usually with the Gunk... sometimes Sea Foam.
Sea Foam is a high power cleaning agent. I dont doubt its ability to clean... but I do concern about it goofing up the oil's lubrication. As a flush at an idle, it gets my approval.