MathBrush is still being built, and it is open in full to a few parent groups while that is going on. The code from the post you came from opens every solution and every question in the worksheet builder. There is nothing to pay and nothing to sign up for.
It is kept in this browser, so you should only need to type it once on each device.
Every solution is open on this device. If one still asks you for a code, that is a bug worth telling me about — shawn@mathbrush.sg.
What is written down when you use a code: which code it was, the days you came, and how many times. No name, no email address, nothing that could be sold, and no advertising anywhere on the site. It is there so I can tell which groups found this useful enough to come back to.