Psion

[Chris Robin R2]

So, I was looking over DSP's Psion, and I noted the Dual Disciple archetype. So, in exchange for losing a couple of class skills and a -1 ML you gain access to a second discipline. Since class skills are just a +3 bonus, I don't think that's a huge loss, and you can counteract the ML loss to disciplines you didn't choose with the Psionic Knack trait (which admittedly, is a loss of a trait).

It seems to me this is, well, almost strictly better than a normal Psion. His power list is very small, so being able to add a second one means having less of a need for Expanded Knowledge. And you don't seem to really lose anything from your primary discipline. You can even pick Generalist for your primary. And I can't think of very many times having access to a secondary discipline wouldn't be useful. Any of them, even rolled at random. 2 is better than 1, as it were.

I mean, is there any reason not to take this archetype, except maybe really really needing both traits for something else?

[Ssalarn]

It's very very close to being a straight buff to the Psion, but you do lose two bonus feats to gain low level abilities, which can be a bit of a loss, and the hit to manifester level does cut in elsewhere. It's good, but I don't know that it's truly straight up better than the standard psion. You aren't ending up with more powers overall, just a broader selection to choose from, and you give up feats that include item creation feats in exchange for some abilities that would be cool at the level you were supposed to get them, but are almost parlor tricks at the level you do get them.