I used to use an FES unit that you put in the shoe and on the tibialis anterior. It was triggered by a sensor in the heal as it came off in last stance and it switched off during heal strike. As to it's effect it depends on the reason for the foot drop.

My early uses were with stroke patients. However I have several other patients with degenerative neuromuscular disease in which it FES is not useful.

For them i use a cast molded Silicon Ankle Foot Orthoses (SAFO).