As an atheist, more power to the Satanists. Their existence means we might become the second most hated group in the religious think space! I say “might”, because Christians are more than happy to see nonbelievers as a bigger threat than other believers, even though we’re an extremely small group. Strangely, TST don’t seem much into Satanism as it’s generally understood. They’re the religious group your having when you’re not having a religious group.
So I’ve gotta say that apart from the rebellious imagery, I’m not sure what Satan is bring to Satanism. They’re not into evil, the supernatural, or even trolling. It’s like the only other option they could come up with was “Humanists Who Aren’t Into Shit Stirring”, but it didn’t sound mystical enough.