The addon ask to create an account but its optional.

works great! it highlight the problematic html element and give explanations and how to fix!
the Exporer tab let you see your website with different colorblind filters.

Very unclear what I have to do to sign in; whether what I have done did it.

It is very helpful to see the critical problems for the accessibiliy and to get some advices how to solve them.

Easy to use, accurate, and reliable. A must have for content contributes, web admins, and developers.