Great.It is really cool. Five Star (5 Star)

very helpful plugin.This is real beauty of FLOSS (Free & Libre Open Source Software)that you get funcionality that is very helpful that too is with source code.& if you are happy with it you may go for Pro Version (if developer is offering) or may enhance by yourself or can hire somebody.
Thanks bro for this very useful & helpful plugin.

One suggestion for system generated code : one more text field not to use certain confusing characters by admin.He will type some chraracter so it will not generate those characters set in code.

Note :
1.I have not checked that whether email is delivered to registered or not since this is tested on localhost.
2. One minor problem in manual code functionality.It creates code automatically in LOWER CASE & on registration it creates automatically in UPPER CASE.So it is immpposible for users to register those user who have manual code.