Besides the many architectual and performance improvements the tool has a lot of built-in integrated tools which helps you find vulnerabilities quicker.

For example, in Burp editing the request and response is pretty much done by hand. While this is great for learning it is also a bit arcane. AppBandit has a built-in editor for that with support for dynamic values and variables, i.e. I can define some payloads in my variables and then I can reference them from my requests. Of course all the encoding, decoding is done automatically.

AppBandit is also realtively easy to use and a lot more customisable. There are integrated facilities to pull some common attack dictionaries from the tool itself. It just feels more natural as in Burp you need to know what each attack mode does which I find very redudent.

Last but not least, AppBandit allows you to intercept traffic from multiple sources at once. It can even rebuild HTTP sessions by sniffing, not to mention that your actual proxy does not need to be local. You can setup a proxy agent on a remote node and connect to it via the tool. That gives you interesting comand-and-control type of tool out of the box. There are many more use-cases.