I find the comments here very interesting, but wonder how many of the contributors have actual experience, or whether, as I find is often the case, it’s just opinion or hearsay? I have been a pumper, mainly cock, for over 35 years and so far have not suffered any ill effects. Although it was initially cock size I was after, it soon became apparent that pumping was a poor way, for me at least, to obtain it. It has been very long term. However, I had, by then begun to enjoy the sensation of pumping and the resulting feel and look. A few years ago I went through a phase of pumping my balls as well, but because of the resulting bulge, very noticeable, I sort of lost the habit. I have recently started again though and am enjoying it immensely, wearing baggy clothing to cover the evidence. The process required, to achieve a size that will gradually dissipate over a day or more, knocks some of the advice given here into a cocked hat. It will take at least a 3-4 hour session, initially, where warm water is an asset. You only kneed to consider all other aspects of PE where heat is recommended to see that. It’s also advantageous to use a heat pad to keep the water warm, longer. I appreciate the argument that heat is not conducive with good sperm production, but we’re only talking normal bath temperature here. There again it depends on your outlook; if like me you’ve had a vasectomy or aren’t interested in producing offspring, it a bit academic. However, with our ball sacks, or rather their contents, being even more delicate than our cocks, they do demand more respect and gentler handling. Therefore there should be little or no discomfort at all compared to penis pumping. By this I refer to the area where the cylinder may dig in. I use a BallMaster and the aperture is considerably bigger than on my conventional cock cylinders. The BallMaster also has a broad lip to spread the load and although you can buy a cuff that acts a cushion I found the cuff I have problematic rather than helpful and at the low pressure you need to work at, between 2-4Hg depending on comfort, unnecessary.
Like I say, I don’t have a great deal of experience at ball pumping, but there are other sites where guys have. These include newart.com, where they run a verity of dedicated pumping forums, and vacpumper.com, a video chat room where guys congregate to pump and display their equipment… both kinds.