Those clasps work well on some sporrans. Buzz Kidder uses them in his sporrans (which I have two of and like a lot) There are two sporrans in that book as I recall. Since you mention using a thong and toggle type closure I'm expecting you made the Rob Roy style that is more like a soft bag. These magnetic clasps may not work very well on those because the leather is so soft and moves quite a bit and the magnets are not strong enough that they would pull together without being lined up almost on top of each other. However, once the bag is cinched up under the flap and since the flap is molded to a fixed position, perhaps the magnets would be close enough to engage on their own or with minimal fiddling. I'd be concerned that with the bouncing and swinging of the sporran though that it would tend to pull apart easily.