Advantages/Disadvantages to a holy order

[Dufflebags]

Just got the option to found one. What are the benefits, if any?

Also what are the difficulties they might present? I'm kinda trying to reunite Britannia as Ireland and I'm running out of time at 1350 and don't want any huge detriments to my cause.

[The Former]

The ruler who founds them gets to hire them for free, I believe (assuming they're ever available). I believe there are other benefits too, but it's been a while.

[Heraclius Caesar]

Advantages:

Like knight-errant said, they're free to hire for their patron.

They'll pay you a lump 750 gold when they request to lease a holding from you.

They are an excellent auxiliary army for your holy wars, just raising them with your men at arms gives you a very fine army to take fire and sword to the heathen.

They can grow very large. I'm unsure of the cap or if there is one, but I've had them at nearly 20k, so that can be a substantial free army for you.

Disadvantages:

There aren't very many, but there are a couple from what I've seen.

Often, your vassals will have them hired out for some lengthy stretches so you can't hire them yourself.

You can't hire them for crusades, they ostensibly go on their own.

Can't use them against members of your own religion.

Also, and while not necessarily a disadvantage for you, for some reason they never upgrade the holdings they lease from you.

[captain403]

They won't fight anyone whose religion isn't at least 'hostile'. So if you are insular christian, they won't be any use against Catholics. But they will (I believe, though I may be wrong) fight heresies (I.E. Cathar).