Password Checkup by Google alternatives

When I requested a log in to developer area (which I assume is how any Byepass login would work) on my mobile, I thought it had not worked and having tried it on my desktop I now realize what had happened.

I did not realize that the original screen I had logged into had changed to show the contents because the mobile window/ screen telling me that the challenge had worked was blocking it (even though it was still there).

I presume that your use-case is that a user would request login on a desktop and then authorize the email challenge on their mobile. In this case it would work perfectly as the the original descktop login request would be showing logged in content.