The Grail has 4 attacks and 6 wounds, it is accompanied by 6 pilgrims with 1 attack and E wound each, it costs 118 points.
The same attacks and wounds for normal rank and file (let's say Men at Arms with a standard bearer and musician) would cost you about 70pts (roughly)
So I guess the question is...
What is the value of being stubborn, having hatred and the Lady's Blessing on a unit with a leadership of 8 ?
Well, let me put it this way... It's worth nothing if you put a small unit of 6 Pilgrims with a Reliquae into battle because they will not win you anything (you'll just be waiting for the inevitable destruction,and it will not take long). They are only capable of holding up the enemy for a while and that's the key !
Holding up the enemy is what the Reliquae is all about with this unit. It's not purely for the sake of obstructing the enemy's plans but to lock up enemy units to benefit the rest of your forces. You can do this in two ways:-
1) either use the reliquae to protect your flanks or
2) charge into combat with the reliquae to give your knights the opportunity to flank charge the enemy.
Whichever you choose, keep the reliquae as close to your general as possible, they really need to roll using the general's leadership because they will be taking frequent break tests.
A few important things to note :-
1) using the Grail Reliquae will slow down your advance because you will want them to be accompanied by a unit of knights for flank attacks and preferably one with a leadership of 9 (the Grail can use the leadership of any Knight within 6" - peasant's duty)
2) The Grail is a holding unit and will be taking a lot of damage. Bolster the unit with additional pilgrims (they cost 9 pts each - which is about the lowest you will ever spend for a stubborn warrior). This unit will not be routing anything but the weakest of enemies but it doesn't have to, you're Knights will be doing that. You just need to make sure they can endure some punishment for a few turns.
3) You have to employ at least 1 Grail Knight of character with the Grail Vow to be able to use the Grail Reliquae.
So, should you use the Grail Reliquae in your army ?
Well, for a 3000 pt army the answer is a definite yes.
For a 2000 pt army it all depends on who you're facing and what tactics you have in mind.
What I am confident in saying is that The Grail is worth paying the points for.