They are like anything else. May work for some, not for others. Depends on what you're looking for, personal preferences and any particular issues you may have. If NON-absorption or clots are a problem (think too thick e-liquid) they are a godsend. An issue pads, tampons and sea sponges unfortunately don't address for those faced with the problem. Should shorten duration for those women as well since there isn't anything working essentially as a plug that just prolongs everything. If you have to use tampons longer than about 4 days, start checking them or use pads a few days.
If you do a lot of swimming, the fact that they don't absorb anything and there is nothing to worry about showing make them a terrific alternative. Much like a swim diaper vs a regular diaper. Containment for what needs contained without anything bogging you down. LOL
Also if you have to use the bathroom frequently for any variety of reasons you don't run into the same issues with needing to change out as is often the case with tampons.