When you land on mt-usw.appiersig.com, you get a 404 error and not much else. That's a problem. Legitimate businesses have working websites with contact information, about pages, and some kind of online record. This domain has none of that.
There are no mt-usw.appiersig.com reviews anywhere, because the site doesn't appear to have ever been live with content. The question 'is mt-usw.appiersig.com a scam' comes up naturally given the complete lack of transparency. The domain owner's identity is hidden, and there's no past history in the Wayback Machine to show what this site was meant to be.
For any site that expects visitors to trust it, these are major red flags. A real operation would have a clear purpose, a way to get in touch, and a visible track record. Until mt-usw.appiersig.com actually shows what it does and who's behind it, the safest assumption is to avoid it entirely.