I use both, the Simple Green product imo is better suited for aluminum, and fool proof. It's also better on painted surfaces, especially in my line of work. Regarding cost, it depends. I'd rather pay a few $$ more when it comes to my Jeeps and use the SG product, the old E-150 gets PP. Some people feel $15+/qt boutique oil is better than Super Tech oil, both are effective and get the job done. I wouldn't criticize them, they have their reasons, just like I have mine.But is it as effective and inexpensive as Purple Power?