This one item gives judicator awesome power. The reasons.
1. The attack speed stacks and 40% is a great boost
2. Mana regen allows for you to spam spells more
3. Cooldown allows for you to fire off a large amount of reckons in a short amount of time and allows for you to use intervention more frequently.
4. the ability power from this item is enough of a boost to allow for two things.
I. Your reckon will beable to do about 500 damage preshot(level 16-18) if you spam this weapon or get any other ability power items.
II. Your ultimate ability will not only have the huge boost from the attackspeed but it will have an increase in damage.

Based on the games i have played since yesterday with this build, I have won each one and I have got my cooldown for reckon to 5 seconds and intervention to 15 seconds. My ultimate was around one minute. I would crit for about 400 and be able tochase down any hero because they couldn't get unslowed because i could spam reckon and divin blessing.
Try this item out on judicator

Nashor's tooth doesn't stack, as far as cooldown reduction goes. But just one of them is really good on her, I'll agree there.

Nashor's Tooth stacks with Stinger, if you're so inclined.
I'm not a big fan of Codex, so I do this occasionally.

Cooldown for Intervention goes all the way down to 12 seconds with 40% cooldown reduction, which is easily attained with Talents/Runes and one or two CD reduction items. This will also result in permanent slowing with Reckoning. Great for chasing.

Nashor's tooth is, I believe, an essential part of the caster build for Judi. Cooldown reduction is key to chasing because it lets you slow a target permanently (or close to permanently).

If you're interested in Kayle, feel free to contribute to the guide here: Into the Fray: a guide to Kayle, the Judicator.

A.