Well it all depends on the material composition of the shield. If we assume a bulletproof titanium alloy, such as the one used in protective inserts for modern military bullet-proof vests, that shield could be quite effective. You could theoretically pull off class IV (Able to stop a 30-06 Springfield AP bullet fired at rifle velocity) or greater protection depending on the thickness of such shield. I doubt your average human would be able to run with this kind of shield for long periods of time however. With that said, if you spread the effective thickness of material between the shield and armour of the knight, you could be really well protected, especially with the added benefit of spacing between the armour layers. Your mobility would be pretty bad, but you don't see Iscariot knights running around for a reason.
As for it being felt or not, if the guy is standing in a hallway, bracing for impact, his arm would definitely feel it, but he could in theory stand through the impact. Unlike a bullet-proof vest, the shield is resting on the ground giving it added support, so with his body properly angled behind it, the guy has a good chance of standing through a good few rifle hits. Considering the fact Fargusson is using 2 pistols, the guy should stand through it with relative ease.
A pistol is pretty useless in this kind of situation considering your class IIIA vest which still fits under clothing can stop a .44 magnum FMJ bullet at least once. Assuming a full class III shield (Rated to withstand the impact of at least one 7.62x51 Nato M80 ball bullet.) + spacing between the shield and body armour + at least class III A armour covering most of the body = A line of Iscariot troops can shrug off at least a good few seconds of sustained fire from most modern small arms short of a .338 Lapua Magnum sniper rifle, and even that would need to punch a lot of holes in the shield before being able to reliably penetrate the body armour.
I think it's pretty safe to say, in this comic Iscariot is much easier to kill, than they would be with all rules of ballistics applied.