For the first two issues, while Super Sons started charting at a lower position than Justice League, they ended up charting higher later. Before the new releases hit, Super Sons finished ahead of Justice League.
Let me see if I can track down the screenshots, because I probably posted them in this thread.
As long as the book is selling more than Ms. Marvel, and books that have shown to perform better than Ms. Marvel, it's safe to say that it's still selling very well digitally.