In the Inquisitors Handbook Imperial Psykers have the option to take the Templar as an optional career rank.

Now, it becomes available at Rank 4 which the rank where you have to make the choice between Militant and Materium. It mentions that " It is likely...you will advance several ranks in the Savant Militant path" Yet it does not mention that you have to travel that path as a prerequisite...

So could you go the Materium path?

I'm also struggling to find what you notably sacrifice if you were to go the Templar path.

Well, if you're going down the militant savant class, you're getting some (most) things earlier, with a few things slightly more expensive, overall ending totally better overall. YAY!

If you were instead considering going down the Materium chain (which, unless the GM allows it, forbids taking the Templar Calix), you're losing out on one Psy Rating increase, several bonus Psychic Powers, and I believe some Power Wells? Maybe discipline? Frankly, you're sacrificing some of your psyker versatility for kickassness in melee. Extreme kickassness in melee. Ungodly kickassness in melee.

Templar Calix is essentially better than Savant Militant at force swording, worse at psychic powers.

You definitely cannot take Templar Calix and follow Scholar class, it specifies alternate rank 4: Savant Militant.

At Last Forgot said:

Howso worse in the psyker department? You can still take all the Militant branch advances, you just tack on extra experience for the Savant Militant section.

Well, the Templar Calix isn't much worse than the Savant-Militant in general.

But the Scholarly path really is vastly superior when it comes to psychic powers. It really makes the choice of which way to go with your psyker a difficult one.

I know I usually prefer tp destroy my enemies with psychic might. It's extremely satisfying, whether it happens with my pyrokinesis or because I accidently opened a Warp rift with a botched roll.

At Last Forgot said:

Well there goes that idea, I was really only interested in blade based advances, along the line of a very humble monk style and considering what the Militant path gives you access to that I wouldn't be taking advantage of....

Consider consulting with the GM, as I did, and try to get a more restricted and costly list for a more Scholar-balanced (HA! As if) approach.

The costs need to be sufficiently high in order to make taking these kickassedness-in-melee talents a difficult choice over becoming the true master of the warp the Scholar path allows. Heck, I'm nearly rank 6 and I still haven't taken Lightning Attack...