I didn't read it that purchase was necessary. I read it as one entry for every $20 purchased, one entry for following and posting the link on Twitter, one entry for Facebook and one entry for the survey. Sure, if you spend a bunch on roadid products, you'd get more entries, but it's certainly not required. Actually, doing the donation for the same amount would give more entries than buying product.
Myself, I have three entries and no money changed hands.