I do have several ones.
A: My first double ballon was the rubber model from Beth Tyler, wut is was not really satisfied with it:
1. It´s size is very small, and you are allowed to inflate it only to 4 pumps with the balloon.
2. It is very very soft, and therefore hard to insert (bends all the time)
3. The natural rubber is sensitive to oil and most oil based lubricants, so extreme care has to be taken to not harm it.
B: The second one i have is the double ballon "Gaul" model from Ruesch (german maufacturer)
This one is better, is has more stiffness so you can easily insert it.
But it does also have its drawbacks:
1. When it gets older, the inflation hose becomes loose at the point where it is ealed to the small "control balloon"
2. It has only one shared inflation line, that is used for both the inner and outer balloon. So, if you pump it up far enough that you think it is OK, and you get a cramp or just the colon tightens, the inner balloon is compressed and the air goes into the outer ballon, and then the larger outer balloon pulls out the smaller inner one - a mess !
Fortunately, the #2 Problem can easily be "repaired": I just put a cable tie around the outer balloon and secure it with two drops of glue - voila, fixed maximum outer diameter, and after some certain point you pump air only into the inner balloon as it should be.
C: I also tried the Beth Tyler "F2S" silicone 500 ccm nozzle.
This one was a perfect fit, hard enough to insert, soft enough to stay without complications.
D: The "F3S" i tested too, bot for me this one is uncomfortable to wear. Even when not inflated or only a few strokes inflated, its tip constantly stimulates the urge to expel, not very funny. Otherwise a good nozzle, maybe my end colon is too short.
E: Various far-east pump nozzles, single- and double-balloon-style: None of them was worth its money (even given that most of them were cheap) - incredible bad quality, probably intended for just one-time use. Forget those!
So, my conclusion would be: get the F2S od the Rüsch one !
The Rüsch is more durable (and cheaper), but the F2S is way more comfortable to wear.