So, I've been utilizing the magnet method for over 2 years now. Here is my personal experience:
1.) The more you use, the more opportunity there is for the magnets to stick to each other and potentially damage your paint/armor. This is especially applicable when storing the pieces in your crate. This is mostly in regard to the shoulder bells and chest pieces. I recommend vertical strips of Velcro on the shoulder bells to keep them from flaring out. These are typically light and durable pieces and do not necessitate magnets.
2.) The knee armor is an ideal place for a single magnet on the front side of each piece. My FP knees are fairly fragile, especially since I use heavy, metal greeblies. The magnets take all of the weight, leaving the elastic bands in place for aesthetic purposes only.
3.) My collar and back piece are separate, and though I use screws, the collar has a tendency to pull against my neck with the weight of my jet pack. Using magnets on the collar hold it well in place, making for a more comfortable troop. I suggest stronger magnets for these type of high strain areas.
4.) You do not need to secure magnets to the flak vest itself. This is a useless step, so don't waste your time. As long as the other side is securely fastened to your armor, these will remain in place. It also allows you to make minor adjustments if need be, as previously mentioned. I actually place thin pieces of scrap metal to the back side of the magnets on the center of the chest to keep the spacing consistent; preventing the closer pieces from overlapping one another.
My biggest problem has been the magnets pulling off the armor itself. I usually have to re-glue a magnet or two every other troop. I have been unable to find a strong enough adhesive to prevent the metal from separating from the plastic. I have tried Gorilla Glue, hot glue, bSi epoxy, etc. Does anyone have any recommendations on a better way to adhere the magnets to the armor itself?
FYI, I am a medical professional and do not recommend use for those with a pacemaker (as asked previously). Also, it ruined one of my credit cards.