Since you can't put both of them on a single phantom, is there any reason you would use the stygium particle accelerator over the advanced cloaking device? It just seems like a wasted card. It has a good ability, but why use it when ACD is available?

Well there is the cost, acd is 4 the other is only 2, plus spa gives you an evade when decloaking as well, so it's almost-but-not-quite half as helpful twice as often...

You see occasional lists trying to make the Particle Accelerator work, but ACD is generally considered to be a FAR superior choice.

If you have low pilot skill, then Particle Accelerator might be a good thing. I've used it in a 3 phantom build to some degrea of success. Might not be the most competetive list, but it sure is fun!

If you cannot recloak before the enemy shoots at you, then the only benefit from the Adv Cloaking Device is from the added maneuverability.

Added maneuverability is not as good when the enemy moves after you.

Thus, on a low PS ship, Stygium is better, as its effect is consistent.

Is this a rules question, or a build question?

Because 30 pts for a hlc with 2 focus and an evade is about as cheap and arguably as survivable as a hlc b wing...

in short. Echo or whisper want acd, as they ability and PS make it worthwhile, sigmas want spa, to set up alpha strikes and very strong attack runs. Plus 4 dice plus an evade token can be extremely helpful last round of an event.

As noted ACD costs more and doesn't do a thing for a ship until after it shoots. If you play the lower PS Phantoms this can be an issue.

Ok, thanks for the input.