I haven't went through the code of this one yet but I know the script it is based on. I made my own version of this as well because the original version is insecure. I hope you've secured this one!
In this project, main drawback is any masters can also delete the Admin or the Super User. So accessing of Admin profile by masters or agents should not be encouraged.
Nice this script, but when i open at admin.php i don't find "update user level level" 8 i found only 1,2 and 9 level ?