It looks primarily useful if you’re submitting magazine pieces or shorter fiction, from what I can see. I think, unless you’re submitting dozens of articles and short fiction monthly, following them on Twitter is probably a better plan than paying for a membership. A 7-day free trial isn’t enough time to properly evaluate their services, in my opinion, and while $5/month or $50/year isn’t a lot, it’s significant if you can’t deduct it as a business expense.
For me, since I write mostly longer fiction. I’m not sure I need a service to help me track submissions or check on open calls. If that ever changes, though, they do seem reputable.