Thanks to lots of time at home during the pandemic, I decided to dive into ball stretching. I initially explored via hardware store options, settling on a set of eight chrome rings with an inner diameter of 1 ½" and a combined stack height of about 2". The main issues with those was the light weight (less gravity induced stretching) and that I had to apply a small wrap of electrical tape around the weld points so that it wouldn't snag hair or skin.
I ended up buying the following:
Both sizes of this kit https://www.pumptoys.com/catalog/All-Products-7/Ball-Ringer-Kit-10.html
A lot of these products can be used together in different ways, not just during sexual activity.
The Tantus cock slings can be paired with the Tantus ball stretching ring set, though with the smaller sling I can only use the larger of the stretching rings due to the height the sling adds to the stack, whereas the larger sling can be used with both rings because the rings fit and nestle within the sling's opening. The latter setup is more enjoyable due to the added stretch and the overall constriction of the whole package. A bit of lube is needed to help prevent skin getting caught when things are so snug down there. On some circumstances the combined constriction of my penis by the cock sling plus the upward pressure of the stretching rings on the ventral side can pinch off blood flow or nerve sensation. Some adjustment can also be required if the sling pulls down on the suspensory ligament. This configuration works great for both anal intercourse or toy play.
I've also tried combining a cock sling with the ball ringer kit. The 2" rings shift around the scrotal sac a lot, which some people might like, but I find it noisy and distraction. In order to take advantage of the extra weight of the 2" rings vs. the 1.75" rings, I've added the Tantus stretching rings to that configuration and the 2" brass rings slip around the silicone rings perfectly. Depending on a given day, my arousal, the temperature, blood flow, etc. The 1 ½" restrictor ring for the 2" set allows my left testicle to escape too easily. In that case, I just finish the stack with a 1.75" ring and the respective restrictor ring.
I could handle all eight of the 2" rings (one pound weight) from day one, so incorporating the cock sling increases the stack height over 2". I've moved up to incorporating four or five of the 1.75" brass rings into the stack in an alternating manner, which adds additional height and weight, boosting them to something like 3+" and 1.5 pounds. The maxed stretch and weight configuration is best for toy play when there isn't a lot of swinging or thrusting motion. Too much and lube spreading around the area and it's not uncommon for the left testicle to “escape” under the forces. However, a gentle thrusting into my hand's grasp while wearing the maxed stretch and weight configuration, and the Tantus Piggy in my ass, is a mind-blowing pleasure experience. For anal intercourse, finishing a shorter, lighter stack with the 1.5" restrictor ring always the ring to get out of the way of the receiver's ass cheeks and helps to prevent a testicle “escape."
All said, the ball stretching and weight increases my arousal on their own, but paired with a cock sling or cock ring helps to take most advantage of the increased blood flow by constricting it in the area, which adds noticable visual girth, that also provides an even tighter fit once in the receiver's ass.
Edit: I forgot to mention non-sexual uses…I've tried walking around, jogging, yard work, etc. wearing various configurations and they work to varying degrees. Too much weight and stretch during a vigorous activity can be uncomfortable or lead to a testicle “escape” but the right configuration for the right activity increases the anticipation of forthcoming sexual activity.