I suspect that the basic design of this device was defective for the simple reason that due to the syringe, the liquid could only be introduced far too slowly into the powder. The instant that enough liquid came in contact with powder that ignition was achieved, the flash blew all remaining powder away, thus rendering the device useless as a destructive device beyond the resulting flames.
Let me add that in order to destroy an aircraft of this size, the bomb would have to disable some critical structure or control system. Placing a small amount of explosive next to an outer wall would result in a hole, loss of cabin pressure and maybe some passengers but probably not the loss of the aircraft. Placing the bomb in the crotch implies that there is a leg between the device and the outside wall, something that only reduces the damage to the aircraft.
(Makes damage to the bomber guaranteed, but to the airplane not so much, in this case, that is exactly what happened.)
see also: http://internet-haganah.com/harchives/006712.html