Prior to joining BITOG, I was (am) a user of Tufoil. Based upon this site, I was thinking the engine would likely implode, but our Camry had 350,000 miles (donated to charity) and our Lexus has 210,000 miles on it. If the Tufoil does cause problems, I will report back with that fact; however, my use since the late 90s -- no problems to report.
As always, YMMV.