So I think the enchantments on the mask have some flexibility - most so if I think of cooler shit, I can sub it in lmao.
The mask can carry a glamor to disguise Na'im - the disguise can be an whole ass full body illusion or just simply making the mask itself look like just a normal fabric facemask. It turns casual attention away from Na'im. Unless people are REALLY paying attention, they won't really notice him. It muffles some of the sound around him so he moves quieter. He's harder to capture on camera - he's blurry or obscured in some way. The effects can be amplified to some degree, but it takes more out of Na'im so they try to keep each effect at "just enough".

Extra: All of the Silver Asphodels have a brand or tattoo, which lets Bijan track their locations and "encourage" them to return if they're not where they're supposed to be (read: hurt them). Na'im and a few others have a worse version with varying levels of compulsion enchantments added in. The mask can amplify every effect the brand has on Na'im and ensure it works over much larger distances.

I got no measure of the blood it takes. As much as it needs is probably the easiest answer.