While we technically CAN take it, I'd avoid it.
Lets put aside the fact its pretty darn bug, and really hard to place on the table due to how fortifications are placed, so often you wont get to place it where you would have wanted to-but worse, in a dense table, it gets automatically destroyed during deployment. the rules for placing fortifications are dumb as they get and fortifications as a whole should be avoided until this is remedied.
The crown basically does 2 things
1-gives a 5+ invul aura to chaos units.
2-gives reroll to chaos psyker tests in small-medium area, and turns ANY doubles to perils in a large area to non-chaos psykers.
Now, while the second rule is quite helpful if you got a handful of psykers within range of the crown, and the more the merrier. now if you have a handful of REALLY important spells, that you can cast from the backline (or wherever you got forced to place the crown), great. but for any frontline psyker (like our princes for example) the crown doesn't do much. for midfield sorcerers too. it depends on you sitting back and shooting/magicing.
The first rule however, does almost nothing for us. most of our units (at least any worth taking. no you do NOT take predators, contemptors and such in 1ksons if you can avoid it, because multiple other armies that are better to begin with has strictly better versions at the same cost. stick to the few things we actually do have that nobody else has a direct counterpart) have built-in invul already. rubrics, scarabs, sorcerers, princes, even goats.
So the invul aura is practically useless for us. building a dakka gunline with generic non-rubric non-scarab marine units will not work out for us ever,
In addition-do you notice a word missing in the rules?
The word is "friendly".
The crown gives the same bonus to any enemy chaos player you happen to come across!
And they often benefit more than you do!
Once the enemy plague marines, or zerkers, or heck even cultists hit your lines, THEY get an invul, once enemy chaos psykers get into the zone, they enjoy the buffed casting too!
You pay, and they reap equal and sometimes greater benefits.
Sure, not every opponent is chaos. not even half. but it will come up at times. having a rule being not helpful except in certain matchups (like DttFE) is meh, having a rule outright help the enemy when in the wrong matchup is horrendus.
The army that has the most to gain from the crown is the renegades and heretics. who are currently not an existing army.