Feelings regarding the magnetic snap closures are mixed. They are super convenient for children's clothing, especially those who are learning to dress themselves. No buttons and buttonholes to maneuver and no hard to secure snaps to get frustrated about. For this purpose, I recommend, and rate rather highly.
For adults if the fit is snug, they do come apart and possibly in a shouldn't be seen area, exposing more than is desired. In these circumstances, the rating obviously drops.
In any situation, these do remain hidden, so you have a flawless appearance using most fabrics. They are easily inserted and sewn in most locations of your garment. I prefer sewing them in place so there's no chance of them moving.
I'm also going to try a set in a journal project to hold it closed.