NezPass may be less secure than LessPass.com because the form submits to the server and returns back the generated password. We employ the same algorithm used by LessPass.com but the inputs actually enter the server. We only store the master password and the password criteria for subsequent use.
It is probably a good idea to have additional secret characters that you append or prepend to the generated password. An example is to add special characters at the end of the password and use that. This way, even if someone snooped while you were generating the password, they would have to guess the additional characters that you only know (unless they have a keylogger)