Brexit Millionaire is not a broker - you can see all of the usual signs that they are not a legitimate firm or app. They change their website URL and domain name constantly and run affiliate fake adverts across fake magazine using plagiarised news from sources like the Washington Post and New York Times. All of the reviews follow the same format and the app itself is not available on Google Play or Apple Store.
The website just forwards you to an unregulated broker who will take you to the cleaners.
You can see an example video of
Brexit Millionaire sign-up fraud on that blog post by sircles.net.
Steer clear of these get rich quick schemes as they are all fake.