I think this is a no brainer, however please confirm the following:

If you hit with a Two Handed Weapon (CR2), and roll two boons in the process, you now have the option of expending these two boons in order to add a Critical Wound correct?

To be specific, you need to expend the boons in order to get the Critical Wound correct? The other interpretation is that if you roll two boons, you get a Critical Wound automatically, and you can still spend the two boons on an action effect.

I believe you expend them on the Critical Wound, however I am still trying to reconcile why you would ever take a Two Handed Weapon over two Hand Weapons instead as the damage potential seems much higher for duel wielding given the available action cards.

Whammo

Yeah, boons can only be spent once, although if you have enough from a single roll, they can buy several different things.

If I'm fighting knights in full armour and shields, or a dragon, I'd want a two-hander.

My understanding is that yes, the player must "purchase" the critical strike with the boons. As I understand it also, this form of critical does not stack, so if you triggered a critical already from successes, this wouldn't convert anymore wounds to criticals. I.e. you'd want to spend your boons in another way if you want.

You may also "purchase" the critical strike from the weapon with a Comet, but either way, it may only be purchased a single time. You couldn't get a critical from the Comet and from using boons equal to the CR.

A two-handed weapon with their high-DR and low CR are excellent weapons. Keep in mind that there is currently only 1 "dual-wield" attack action, which is double-strike. Hitting with both weapons (ie, using both DRs) is certainyl not guaranteed. The 2-handed weapon will consistantly deal more damage per hit, as well as the easier CR2 to inflict a critical. There are also some nice 2-handed weapon only attack actions. Those mechanics aside, a 2-handed weapon user can free up a hand to perform other maneuvers, while a dual-wielding user would have to a weapon or spend a maneuver to sheathe, if they needed to use a hand for something else.