I don't know if there's anything wrong with Sheildsup (other than my recollection of it being a pretty run of the mill tool for reporting open ports), but the guy who makes Shieldsup is, in my opinion, basically a charlatan. He writes loads and loads of technical-sounding blather on his website that is very transparently designed to make him look like an expert on security to people who don't know any better. He's made a career out of selling tools people don't need but which are hyped up to make them sound critically important.
Here's an example of some hype I just found about a device he "invented" that is supposed to really put home routers through their paces, because he's the only one looking out for us. [1] Of course, it maybe doesn't exist, and his claims of what it's going to do sound far-fetched and misguided, but it sure does seem aimed to make him sound like a real security expert. Not sure if he ever made any claims about having evaluated any routers with it.
[1] https://www.grc.com/r&d/assimilator.htm
