I saw that one of the authors of the book...seemingly the person who wrote this specific power answered exactly this question on the onyxpath (the publishers) forums.
His answer was:
Dice Pool: If there are no observers, yes. It's uncontested.
Costs: As-written, Show of Power costs the same regardless of the power it emulates. Any cost in Mana, Pyros, etc. is included in the one Aether cost of Show of Power. It's an Exploit, though, so it's going to provoke a compromise every time, and I'd say a ST is within his rights to levy penalties on this compromise roll if a demon spoofs a huge, noisy power (like Tier 3 Utterance) or uses the Exploit multiple times in the same scene (maybe use "number of times equal to Primum" as a "safe" number of uses).
I suppose if the power has an ongoing cost during the power's duration ("while this spell lasts, you can spend 1 Mana to do X as a reflexive action"), it's probably fair to rule either that the extra "spend Mana/Glamour/etc." benefit isn't accessable except with an additional use of Show of Power or to charge a like amount of Aether whenever that add-on is invoked. For some powers where not having to spend Mana (or whatever) won't completely break your game it's probably okay to ignore the extra cost entirely.
Successes: I didn't address contested rolls/defenses. I'd say that if the demon wins the contest on the activation of Show of Power, she successfully spoofs the power. However, she counts as only having gotten one success more than her opponent for the purposes of the effect. If it's the kind of situation that would normally provoke Clash of Wills, run the Clash of Wills separately after determining whether Show of Power succeeds or fails.
What Powers: Show of Power is intended to allow a demon to convincingly pretend to be another type of supernatural being. Any capability the absence of which would betray the demon as a fraud should be reasonably covered by Show of Power. I think I would probably cluster basic capabilities under a single aegis for the sake of simplicity - one Aether to take on all the qualities of a corpse (bashing damage from bullets, doesn't breathe, etc.), one Aether to render your blood addictive (allowing a blood bond that is very real), etc. The changes only last a scene, which limits the Exploit's utility somewhat, but I'd say the effects (the blood bond, a spell whose duration hasn't yet elapsed, etc.) can outlast the demon's ability to recreate the effect without another use of Show of Power.
The post was this one: