I have the Carbon Arms dummy rounds. They are a good value for their intended use.
The following is from their website:
There are a few things to realize with Dummys in normal 12 gauge hulls.
1. They do not have an infinite life. We have had a few guys send a few back and the shells are completely destroyed. Chambering shotshells, of any kind, will only let them last so long, especially if your shotgun has any alignment issues.
2. Keep them clean. A few we got back were embedded with dirt, in the crimps and the hulls. Putting those in your tube or chamber, no wonder they were not feeding well.
3. Dummys are meant to practice loading primarily, not use for shooting drills and "dryfire" like snap caps. ALL of them will eventually have damage to the rim and primer if you use them in that manner.
We seal the crimp, but some gear maintenance, like inspecting the crimps once in a while, is a good idea. We seal them with a clear silicone, which you can easily redo. I have a set of 4 that have been loaded a lot, and they are still pristine, but I don't drop the firing pin on them nor do I chamber them.