The site and powersim are both legit. I see no reason for Norton to flag it other than it relates to gambling.
Powersim is useful because it's accurate and completely open source, so it can be easily changed for unusual circumstances. For example, I used it to verify my partial info HC strategy, as well as a few promos with unusual rules ~10 years ago. The language xbasic is truly awful, but it gets the job done.
As for the average bet, it's probably including your $0 bets as part of the average.