Another thing is that I have seen some real horror stories from people who have used this in a severely neglected/sludged engine. Seafoam is a very good cleaner and breaks loose all the crud at once, plugging oil passages and causing serious harm.
A more gentle flush is Marvel Mystery Oil which I understand is basically kerosene. I have no issues running Seafoam in an engine that has been cared for but would pick MMO if there is an obvious sludge problem.