The magnets will not harm your machine unless you were to cover the computerized part with them! Check with your dealer and they will confirm this! I was skeptical when I first heard about the Magna Hoop but both my dealer and Janome assured me there was no problem. I love the Magna Hoop. It comes in so handy with projects on fabrics you don't want to leave hoop marks on such as suede, velvet, etc. Also small things like belts or pockets are much easier than trying to hoop.
I have investigated the Snap Hoop and so far the price has prevented me from buying it. Hope it drops soon.