Correct. Burp is the main competitor, but it's been around a long time and I wanted to develop something from scratch to address a number of the problems myself and other pentesters have had with it.
Usability and performance (for example when deployed on lower-end customer machines) are two major ones. Admittedly they have been getting better over time.
It's also not uncommon to have sites behave a bit differently when running via Burp, so given it's not open source, it can be hard to diagnose/debug what's going on.