We all bought a mag spark or something similar back in the 70s, it looked the same as the one pictured above. We all quickly abandoned it.
Here is what I found back in the day; perhaps they are better now. First off, they work, no cap popping even on rainy days. These are a one-shot deal, when I used one the 209 primer would expand in the cup when you shot and was very difficult to get out, it took a thin blade sharp knife to pry the spent primer out, even then it took a while to get it to turn loose. For me the overall time between shots would be a couple of minutes after you loaded the rifle just replacing the 209 primer. Handling the firing assembly with cold fingers was problematical as well.
Perhaps they have made improvements since the 70s, if not, I wouldn't buy one.