I thought it was worth writing a quick article about these guys.
This unit isn't quite the minimal unit size for it (at least from points) as it rocks in at 252 points.
You can make them cheaper by swapping out those Castellan Axes for Guardian Spears which brings them down to 246 points.
I would actually like to run a larger unit of these guys moving forwards, but in the short term I will take about how this unit has worked.
They nearly always start in reserve for me, it costs no CP, and allows you to deny a drop as such to the enemy. As Custodians don't have any fully useful Transports as of yet you can't really manipulate your drops, which can mean even though they are expensive you have a fair number of units to put down.
When I drop them in they generally have one goal, and its not always Character hunting (sometimes thats the case!). These guys are there to drop in and lock down gunlines... hence me wanting more than 3 of them.
Their special rule
Now lets compare that to how Pile In & Consolidate normally works
So, it does have a few restrictions, to use their special ability they have to end their move within 1" of an enemy model, where as Pile In & Consolidate just mean moving closer to the nearest enemy model.
Where this ability shines is against gunlines, especially where you kill something you can't easily one shot (say a Landraider Achilles).
After charging it you will be within 1" of it, meaning if you Pile In or Consolidate you will have stay within 1" of it, and this can limit your ability to get into combat with other units in the gun line.
From a Deep Strike you already need a 9" just to get in, so you wont always have that much room to play with either for getting those boys in.
Now however with the Slayers of Tyrants, lets assume someone has a Company Ancient just behind their Hellblasters & Devastators, and those are off to the left, within 3" of your models base. Suddenly you can use the Pile in & Consolidate to get 6" closer to the enemy units you don't want shooting at you!
It wont work often, but when it does its amazing! I locked down two Leman Russ Battle Tanks because of this, where as I would have never been able to without it!
If you want to read something about how charges can work in general, here is an excellent article I found recently from a top gamer that can give you some hints and tips.