Im "avg" size and I've never had any complaints in bed... only compliments.
That being said, after a night of drinking and gambling my now-wife and I went to a sex-shop to spend some of our winnings, and I bought her a new vibrator and I couldnt really find anything I wanted for myself so out of shits and grins I scooped up one of those pumps just for the fuck of it. It didnt do anything for me, however I didnt really use it constantly to try and enlarge myself so perhaps it would have worked better had I really tried. But honestly, like I said im already "average" so I didnt have the overwhelming desire to sit with a pump on my cock for hours on end each day for hopefully a half an inch more in length or so. Just not worth the hassle.