I would recommend a Bathmate, either the Hercules, or the X30. I bought one, started using it at 7 1/4"x5" girth. It got me to 5 1/2" in girth, but no real length gains. I think the problem with the Penomet system is that the lower resistance gaiters don’t produce very much vacuum. I have no complaints about my Hercules, except that I think I have worn the bellows right out, and now it doesn’t produce as much vacuum. But I’m ready to make the move to a Goliath after I take a few months off for deconditioning. I just watched a Penomet vs. Bathmate video on Youtube earlier today. While the tester guy’s technique was flawed at best, it was quite clear to me that the less strong bellows of the Penomet system were probably just this side of useless. I think the Bathmate is better, and also it is cheaper. And that’s my opinion on that.
I wasn’t going to post this link, mostly because this guy is not using these as water pumps, but is air pumping with them, but you can see what I mean by the Penomet gaiters/bellows not being as strong as the Bathmate.