I'm now using the Emcotec arming switch and can confirm that it's a very good product. It's far simpler than plugging in a jumper, is spark free when connecting batteries and the LED in the magnet socket clearly indicates when the ESC is armed. Weight is very low but would not be as low as a couple of bullets and an extension wire etc. IMHO the benefits far outweigh (no pun intended) the weight penalty which I would estimate is ~20 grams.

Regards
Jason.