Maybe the material of these things has changed. Were they more durable back when they came out? It seemed like an interesting idea so I bought on a few years ago. It burst inside me. Not painful, just surprising. Now I don't use anything but the 1/2" tubing and just hold tight to it.
The problem is that people (me included) want to inflate the things as large as practical to seal everything off. There is a limit to elasticity of these balloons whether made of latex rubber or silicone. Once you inflate it beyond its elasticity and the rubber begins to "yield." What you are effectively doing is breaking the polymer chain bonds that give the rubber (whether silicone or latex) its elasticity.
And there is always a weakest point. Always. So, if the balloon is overinflated, it will begin to weaken and loose its elasticity and strength at that point.
I always thought that the two balloons were too far apart to effectively pressure seal from both side of the anus. What I discovered is using a different technique actually seats the balloons quite effectively.
First, you do need to know how many squeezes of the inflation bulb will fully inflated the inner fluted balloon (when outside of the body). And then never go beyond that. You don't have to lose all the fluting at the top of the balloon but it must be inflated and smooth along the length of the inner balloon.
This does require a fairly empty lower rectum to work effectively. With the balloons deflated, insert the catheter and the inner balloon in as far as possible (up to the outer balloon if you can). Once placed, use your internal muscles to "pull" the nozzle further into you by a series of Kegel contractions. I do 4-7. You may or may not pull the catheter further inside you but you allow the inner tissues to begin to "seat" the balloon inside you.
First squeeze of the inflator bulb to begin the inflation process. A series of 4-7 Kegel contractions. The next squeeze of the inflator bulb. You keep repeating this pattern until the inner balloon is fully inflated (I prefer one less squeeze on the bulb than the outside full inflation because my rectum is putting opposing pressure on the balloon). You should notice two things. First, you should feel some pressure of the inflated balloon inside you. Second, it should have felt like the balloon and catheter were being drawn into you. At this point you can actually give the tube a slight tug and it shouldn't move. If it does, it didn't seat and you should consider deflating it, extracting it, and reinserting it. If its a mess when you pull it out, you'll know why it didn't seat inside you. A quick low volume flush should alleviate the problem. Clean it up and try again.
Once seated inside you, you are ready to inflate the outer balloon. With the very first compression of the bulb, you should feel the outer balloon pulled tight against your outer sphincter muscles. That pressure should increase as you inflate the outer balloon(and the inner balloon shouldn't pull out because of the pressure. Since it only takes a few squeezes to inflate the smaller outer balloon you're usually set with 3-4 squeezes.
And then you're ready to go. I like to put a clamp on the arm that feeds the inner balloon on my rubber latex double balloon catheter. After inflating the balloon, the clamp makes sure I don't accidentally knock the inflator bulb off the end of the hose (learned by sad experience). If that happens, particularly with a large enema, the blowout can seem as messy as the blowout of the Macondo well beneath the Deepwater Horizon. I also like to put an inline check valve in the base of the nozzle. It adds a bit to the retention with unidirectional flow into me with the enema solution. It also allows me to disconnect from the bag and the hose while the inflated nozzle holds the enema inside me.
If you don't overinflate and over pressurize these nozzles, the last for a long time. The set I am using now are three years old. But it took weakening and then popping the balloon to learn how to do it correctly.
One more caution: if you are laying on your back while taking and holding an enema with one of these nozzles, be careful when you get up. If you sit up and the outer balloon gets underneath you and your body weight...POP! Either roll over and get up carefully or mostly deflate the outer balloon to get up. You can re-inflate it once you are up and if you wish to hold your enema a bit longer.