nobody is using them profitably, in the long term
that’s the answer to a slightly different question from the one you asked, i know
please excuse me for answering a slightly different question - i do so only because i think it’s actually a much more helpful and much more relevant question 
i’m naturally very curious, and i know that i sometimes wonder about things that don’t seem to bother many people, but i can’t help wondering, if they’re such good traders, why they’re short of $30 per month, or even multiples of $30 per month?
to me, that seems very peculiar
i;ve been trading for nearly 4 decades, and there’s never been a time when i’ve wanted to sell any “signals” for $30 per month, or for any bigger or smaller amount than that, and i’m wondering why it’s what they want to do?
it’s a legitimate question, isn’t it, and rather a puzzling one, don’t you think???
i also can’t help wondering whether their marketing skills might be better than their trading skills?
i also can’t help wondering whether you have a clear understanding of “selection bias,” Paul - seems to me that it’s the ONE thing you need to understand, in this context, before paying anyone a penny to follow their “signals” - it’s explained (and in exactly the context of your original question!!) right here …