Soldiers might or might not like this gadget depending on the terrain, the mechanical resistance of the device, and their own physical reserve. You don't get something for nothing.

30 mW isn't exactly enough. To put things into perspective, a cellphone uses 15-30 mW on standby, and around 2 W when you're actually transmitting. Walking around for an hour would give you less than 30 seconds of talk time.

There's no way around physics - you need power to transmit, or it will be very difficult to hear you.

Well you will get bigger thigh muscles if you do useful work then you wont have to do that particular exercise at the gym :-)

They have to make it rugged enough not to break when the solder take a flying dive to the ground when the bullets start flying, waterproof and sand proof. This could add weight and bulk to the device.

if the load was adjustable this could work similar to regenerative braking when walking downhill. It could take some of the the load of the leg muscles when descending, then be decoupled when going uphill.

It's a good place to start. Eikka has a point, but the idea is to reduce the amount of weight of the batteries carried in exchange for something that will take less energy to recharge smaller batteries than carrying the original weight would take. The entire system calls for improvements in efficiencies of all components except the batteries, for which progress seems fairly slow, unfortunately. They usually put a large amount of thought into new equipment that they make standard for soldiers, but not always. (Seriously guys, velcro on every pocket? There are times something needs to be retrieved QUIETLY in a hostile environment.)