The mod gives you customization options for each power and the summoned entities, be it for example the equipment of both Dremora, the carrying capacity of the Dremora Butler, the merchant gold of the Dremora Merchant or the buffs of the Spectral Drum. The Dremora and the Spectral Drum can be commanded like simple followers if you summon them with their advanced summoning spells that come with the mod.
If you obtained one reward, you can craft the advanced summoning spell tomes for all three rewards (or use the console to start a quest which puts the tomes in your inventory). So it’s no longer necessary to return to Solstheim in order to read the book when you want to choose another power. I never understand why they didn’t give you all three powers at once from the beginning.
The different looks of the Dremora
Vanilla Flavor:

Alternative Look:

A small selection of the equipment options
Practical Pirate (created by QuarantineCouture):


Daedric Light Armor (created by Mihail, edited by me):

There will also be a patch for Zim's Dremora Improvements