Hey all. Great subject.
I've been actively working on stretching my balls for about 3 years to obtain more heft and perhaps feel some "swing" action which is an interesting sensation.
I like using steel rings (of various sizes and weights) that I just slip my balls through. Depending upon my mood I might stack on as many as are comfortable which stretches your sack mostly due to the weight of the rings.
At times I'll wear them for the day but find wearing briefs necessary especially if you're going to be active simply because things happen...
(a nut pops out of a ring and pinches the skin, a ring is loose because you're stretching yourself and there's slack etc., etc.).
I've had somewhat better results with steel split collar rings (it's the "impressive" way to stretch. A word: they have to be a perfect fit for you and the weight isn't adjustable.
In all matters weight is a big deal and one of the factors for a good stretch. Just enough is great, too much and it could be injury.
After all my efforts I have had results albeit minor. However, working at stretching has increased my stamina and truly enjoy some tension but more comfortable.
That being said I'm lovin' neoprene stretchers, ball separators, many of the OxBalls rings and toys, some leather stretching sheaths, etc.
More comfort, looks hot, good results and something for everyone!
Good Luck!