I have two K-frame .357 revolvers converted for moonclips, a Model 13 and a Model 65. There are pluses and minuses to the conversion.
PLUSES:
1. It's much easier to carry moon-clipped reloads in a pocket than rounds in a speedloader - less bulky and no fiddling with speedloader releases.
2. Being less bulky than a speedloader, you can often fit twice as many moon-clipped reloads into a speedloader pouch than you can speedloaders. This is also useful for shoulder-holster ammo containers - they can be made smaller for moon-clipped rounds than for speedloaders, which helps with concealment.
3. They can be quicker on reloads in the sense that the rounds in the gun, being locked together with the moon-clip, fall out together when the ejector rod is pressed. I've not had any problems with one or more cases 'hanging up' in the gun.
MINUSES:
1. As noted, you have to take care to line up the rounds with the cylinder when reloading. In normal reloads, this isn't a major problem, but in fast stressful reloads, it can produce fumbles. (On the other hand, HKS speedloaders suffer from the same defect, so that's not necessarily a problem restricted to the moon-clip.)
2. The rounds can gather detritus in between themselves if placed in a pocket with other items (e.g. a coin, or paper-clip, or something like that). This will stop a reload faster than I can tell it! If you want to carry moon-clipped reloads, do so in an empty, clean pocket, or use some sort of holder.
If you're prepared to train with the moon-clips, and practice (and practice, and practice) reloading them until it becomes second nature, I think they're a very valuable modification. If you don't plan to practice enough (and regularly enough) to master them, it may be less than optimum for you.
Hope this helps.