Is the VPS Bootstrapper program digitally signed? Yes.
Is my password entered into VPS Bootstrapper safe? - The password for the SSH login user you entered is saved and protected by the Windows Data Protection API, which means that by design, it can only be decrypted on your own computer with your own Windows user logged in, copying your database to another computer won't work. - The password for the root Linux user you entered during the new standard user creation won't be saved to the disk.
Is the connection from my computer to my remote Linux VPS safe? Like anyone else who is connecting to their remote Linux server from their local computer, the connection established by VPS Bootstrapper goes through the SSH protocol, which means Secure Shell Protocol - it exists solely because secure connections were needed ;)
Any other security concerns? - Need not to say, you must keep your computer on which VPS Bootstrapper is installed safe.
Also check the Imprint page to learn more about the developer behind VPS Bootstrapper so that you'll be more confident about the trustworthiness of VPS Bootstrapper.
Download VPS Bootstrapper
VPS Bootstrapper gets rid of the command line obstacle of remote Linux server administration for non-techies who prefer a Graphical User Interface.