Can't really agree with what the author is concluding. "Leaving the ans blank won't be penalized much"........No way......
I think her final conclusion is: Low ability—omit; high ability—guess
So basically, if one is say in the 500-650 range, then leaving blank might be better, whereas if someone is in the 650 - 700+ zone then guessing is better.
Not sure, but there might be some merit in what she is saying.