I don't see how this will be useful in any situation. The medic already has more effective body armour.
Actually, I could see how it would be amazing.
As it stands, medics are tanks of a sort. When someone gets close to death, a medic is supposed to use their tough armor to block hits, while they heal their ailing buddy.
The shield could be used in a few ways. Primary fire does a relatively weak bash, while secondary deploys it on the ground. The shield is wide enough to block a doorway, but has half the HP as a normal door, and has a meter (like the heal gun or welder) that ensures it can only be deployed if the meter is full. The meter goes down by blocking (Standing and holding it in front of you) but slowly recharges if you are holding it. The effect being like the welder, it goes down, but at a slower rate than if it is deployed, in which case it will only regenerate if picked up.
If the HP of the shield reaches zero, it falls to the ground and is useless until picked up and recharged.