Disadvantage? I found it absolutely annoying to load up moonclips and much worse to remove the empty brass later. Also, if you aren't careful, you can bend those clips and once you've done that, they'll never be the same.
Moon clips are relatively inexpensive. I have about 30 of them for my S&W 625. I just load up all of them at one time so I'm not loading / unloading in the field.
While expensive, the BMT mooner / demooner is about the fastest tool you can find for loading and unloading moon clips. Takes about 30 seconds to load a moon clip and less than that to unload. There are other tools available from Dillon, and more listed on Brownell's and Midway.
The North Mountain Moon Clip Holder makes carrying additional loaded moon clips easy for field or competition use. With a little practice and moon clip holders, you can unload / load a revolver nearly as fast as a semi-auto.