Let's make this clear right off the bat. You don't need this app. Yes, USB drives can be infected but it's not going to be a big issue for most users. Plus, many antivirus apps already offer protection against infected media.
A singularly focused app
The biggest problem with USB Block is its singular focus on preventing infections via detachable media. While there are threats of infection from infected drives, it's highly unlikely that most consumers will come across these drives.
The more likely scenario is for users to get infected from a malicious download from the web. Since attacks using USB drives requires something to be physically present, it doesn't cast as wide of a net as distributing viruses and malware over the web.
For the same price, you can pay for a subscription to an antivirus application like Avast or Bitdefender, which protects you againsts viruses and malware from all different sources, not just removable media.
Easy to use
USB Blocker is easy to use because it only does one thing. By default, it blocks all removable media until you enter a master password. This can get annoying if you have a lot of removable media. No data can be transferred without this password.
The app also offers a "stealth" mode, which hides any trace of USB Blocker from your system so attackers won't know you're running it.
USB Block also provides detailed logs so you know exactly who's doing what on your computer. The usefulness of this feature depends on how advanced of a user you are.
Buy a good antivirus instead
If you're in a position where you're exposed to potentially infected USB drives all the time, USB Blocker may be helpful for you. However, most users won't need this app and advanced users experimenting with infected drives will likely be running sandboxing software. If you're a normal user looking for computer protection, you're better off buying an antivirus product instead.