The shield recharge rate caps out at level 3. The first one to be placed in an area is the one that is given the XP. If you placed one in the same area as another device, you can destroy the other one and start gaining XP for yours. The device is a good way to have some sustainability against explosive spam ONLY if you are wearing Flak Armor 5. Notice I say SOME sustainability, any concentrated explosions will still kill anyone in the radius.
