Benefit of Shepsi-ak's Funerary Mask for Undead?

[iGMYT]

Can someone explain the benefit of this mask for undead?

Shepsi-ak's Funerary Mask:

An undead wearing this golden mask is treated as both an undead and a creature of the type it was before becoming undead (including any associated subtypes) for the purposes of determining its eligibility as a target of illusion and transmutation spells (such as alter self or disguise self). A corpse wearing the mask gains the effects of gentle repose and sanctify corpseUM. A living creature wearing the mask gains no effects.

Why does this mask call out Alter Self? What does this mask allow Alter Self to do for an undead that it couldn't already?

It looks beyond the scope of the mask to allow you to target an undead with spells that require a "living creature", so then what benefit does this mask actually give?

I imagine if you had an undead Drow you could use Ancestral Regression on it... but this seems so niche it feels like I'm missing something.

[zza ni]

the writer probably didn't remember well the target of these spells and assumed it was like enlarge person that target only humanoids.

i just call it as counting as both for disguise skill checks so he won't take paneities for appearing as a different race.

[iGMYT]

As you say, this item making spells that require "humanoid creatures" work on undead is a great benefit!
Looks like I may need to consider getting the Mask after all. I need that Reduce Person!

Thank you so much for your response.