We believe that it's safe to use a password + TypingDNA than just the password. Most people do not use ANY 2FA today, you are certainly an exception. So are we. We use Yubikeys and Authenticators internally, but this is the kind of solution that can make things more user friendly.
Sure, here: https://api.typingdna.com/index.html (includes usage samples in different languages). You can sign up and find out more... I thought you knew that. Thanks for asking!
In case this wasn't clear: they're not saying you won't generate a model from their Dvorak typing, but rather that the model you generate is likely to depend on the keyboard layout, and so will break if they try to log in from a different keyboard.