I got a 1.75 inches increase using those 'insecure' devices called extenders.. I agree with Big Al, you could rely on exercises alone and do great.. i use this devices because i can do other things at the same time while i am stretching my penis.
Do more reading and you will find great information. I posted years ago here a thread informing of all available options. Check it out! Alternatively, go to the Thundersplace forum, they seem to be the best for this so far, but not the only one.