It was my experience, some call it good gains and some may not (1,1 cm bpel). My "exclusive extender gains" was not any kind of easy achieved initial newbie length gains for me. I started with manual pe back in oct 2004 at 6" nbpel, 6 1/2" bpel.
Now, since I have the space and time alone, I´m doing both manual pe and using my extender combined, and gains seem to come faster.