What disappointed me most about the psyker powers is there is almost nothing in there that a guy with an auto-cannon/grenade launcher/vox link can do. Who cares about your ability to fire mind bullets when they aren't really any more effective than regular bullets. I'd want a pskyer around to do things that can't be done otherwise: deal with warp things/demons/whatever, read things directly out of the enemies mind, provide non-explody battlefield effects (if I wanted explody battlefield effects I could just use tanks or artillery, which are both more effective and more available to the guard than psykers are), transport us in ways that a chimera can't.

So, of the powers listed, I only really care about Gate of infinity, Scrier's gaze, Puppet Master. For everything else, there's a guy with an autocannon with an exterminator gaffer taped to it, who does the job much better and doesn't cause perils of the warp. And the worst part is that the best power (Scrier's gaze) is both the cheapest and the easiest to pull off.

A Psyker with any power behind him in OW is utterly terrifying. Seen one oneshot a Chaos Sorcerer with a single power.

I can see how having a plasma gun that no one knows you have and sometimes summons demons (or whatever) when you fire is is great in, say, dark heresy, where no one know you have a gun can be a great advantage. But in only war, you can just carry a plasma gun (or autocannon, or lascannon, or whatever) and none of those have a chance of summoning demons when you shoot them. I've never said that psyker powers weren't very good at firing mind bullets, but in a game where all of your friends can fire real bullets, it doesn't make you that much different.

So, for example, you have a choice of people to get on your team:

Heavy weapons guy:

I have an auto cannon, I can paste anything up to a tank out to 900 meters.

Psyker:

I have mind bullets, I can paste most things out to 40 meters. But sometimes I screw up shooting mind bullets and summon demons instead.

See how most people would choose the heavy to be on their team?

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See how:

Heavy weapons guy:

I have an autocannon, I can paste anything up to a tank out to 900 meters.

Pskyer:

I has a las pistol, but occasionally, I can see the future in enough detail to know exactly what the enemy is planning. Sometimes I screw up seeing the future and summon demons instead.

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Is actually a choice you'd have to think about?

I've an abject hatred of Psykers myself, and would rather bring an Adept to the Battlefield if it means there's no chance of Perils. Hand the guy a Pict Recorder and he'll probably still have a more net positive effect lol.

A bit off-topic but autocannon, multilaser and lascannon are extremely OP.

RAW, Psykers are supposed to have the same gear as the regiment they're trained with.

I'm a fan of the Telekinesis powers that let you give your whole squad cover. Those can be a big life-saver and are things that other characters can't do.