Moon clips have other issues in real world use that have not been fully addressed above.
They work fine in a tactical match, where they can be carefully inspected prior to the match and carried in speed loader carrier designed to be worn on the belt and hold them safely - and none of those are well suited to concealed carry.
Moon clips also have the potential to get bent if dropped and almost certainly will get bent if stepped on after you have ejected the clip. They can also get bent if just carried in a pocket when the bullets are pushed together.
For pocket carry, you need something like this, with a cap to prevent the rounds from being splayed out to the sides, and a central core to keep them from being pressed together.
It works great to keep the moon clip and rounds safe and functional in the pocket. The downside is that now you are back to a two stage process where you first have to push off the protective carrier before you can insert the rounds into the cylinder. In the end, you have zero speed advantage, and in some cases a net loss in speed compared to a well designed speed loader.
The pressure needed to bend one depends on how thick and how springy the steel is, but they will all bend. Moon clips in general work much better with shorter, larger caliber rounds.
Smaller calibers like 9mm and .38 Special / .357 Magnum usually have thinner than .45 ACP, and the shorter .45 ACP round puts much less bending stress on the clip than a .357 Magnum. That puts .38 / .357 Mag moon clips at a double disadvantage.
Inserting the rounds into the clip and removing the fired cases again is a pain, but also a reliability issue. You can do it with your bare hands, with some practice, but getting it done without bending the clip is problematic, especially with thinner 9mm or .38 /.357 moon clips. You can use a pair of needle nose plies to press them in and that has much less risk of bending one, but you are best served with a specialty tool.
Bending is a big concern as a s bent speed loader at best makes it harder to load the cartridges into the cylinder, and this becomes an issue much sooner with the truncated cone or round nosed flat point shaped hollow points or LSWCHP bullets most people use for self defense than it is with the round nosed bullets shooters are more likely to use in tactical matches. Worst case, a bent moon clip will jam the revolver and prevent a reload as a proud standing moon clip won't allow the crane and cylinder to re-enter the frame. I've also found that some moon clips and some revolvers don't get along when the tolerances stack the wrong way and you end up with a new moon clip that won't allow the cylinder to enter the frame.
The saving grace is that moon clips are relative inexpensive so you can load up a couple hundred rounds at home prior to a range to avoid having to reload them at the range, and then keep them safely stored on spindles in box, until you either load them directly, or place them lovingly into your totally impractical practical pistol match belt and carrier.
But you need to understand that upfront and buy 50 or so moon clips when you get the revolver. The 5 or so that come with the revolver won't satisfy someone who actually likes to shoot revolvers rather than just look at them. A large number of them also covers you when you inevitably bend some of them.
That said, the saving grace about most moon clip capable revolvers is that most of them can be fired without moon clips.
Most 9mm and .45 ACP revolvers for example still have chambers that are cut so that the cartridges head space on the mouth , just like they do in a semi-auto pistol, so they can still be fired without moon clips. That allows those revolvers and their rimless cartridges to be single loaded.
Most revolvers with rimmed cartridges like the .38 Special and .357 Magnum have the cylinder face relieved to accommodate the moon clip. However, the moon clip itself does not encompass the outer portion of the cartridge. That allows the outer portion of the cylinder face and chambers to be left uncut, so that a single round can still headspace on the rim without a moon clip. That then lets you single load rounds, use a speed strip, or use a speed loader, when using a moon clip isn't practical or advisable.
Which is something to consider if you think you might want to use moon clips at the range, and then use a speed loader or speed strips for concealed carry. The downside of this of course for self defense purposes is that you'll have to master two different reload methods, and then default to the correct one under extreme stress if you ever find yourself in a true self defense situation where you also need a reload (which is admittedly very unlikely).
That forced choice of moon clips reflects the reality of many of the "practical' pistol" classes, where the handguns, equipment and techniques being used actually have very little relevance to self defense shooting. That leaves you with the option of being truly practical to take advantage of applying practical techniques under time and pressure, but not being competitive, or being competitive with very little generalization to the real world.
In short, I really thought I'd like moon clips and I really tried to love them. But outside of the very artificial conditions of a tactical pistol match they are the next best thing to totally useless. In my experience, when it comes to real world concealed carry, they are just a liability. Consequently whether moon clips work for an individual shooter or not depends entirely on what the shooter plans to do with the revolver and what that shooter's priorities happen to be. They are currently popular. Whether they will stay that way remains to be seen.
