It lets you pass in two files with the two outputs you want to compare, and lets you set a --diff flag to show a visual diff. You can also configure whether the A/B mapping should be randomised so you can perform an actual A/B evaluation
Alternatively, you can also write a custom recipe and use the diff interface. You can see an example of the expected format here – that's what your stream needs to yield: https://prodi.gy/docs/api-interfaces#diff You can also put together a custom combined interface, e.g. using diff plus choice for multiple choice options, or whatever else you need: https://prodi.gy/docs/custom-interfaces