I have Hakkon, still I don't have this blizzard one.
Hakkon crit damage bonus work in my opinion in best way with:
1. AW, either with SB or without. I'm using build without SB focused on detonating sleep combo with dispel/mind blast so based on spells it's electrical - spirit damage build. Hakkon nicely boosts damage from detonations and even this mana cost reduction is quite handy on AW.
As for the upgrade, crit chance for me, I have too low cunning (51) to just stack crit damage.
2. Ele with fire mine and chaotic focus (or other ele with more direct damage spells).
My build is fire wall, fire mine, barrier and fire storm, so Hakkon is mostly here for:
a) to get other type of damage to not be pure fire

to boost damage of fire mine
Fire mine with chaotic focus can hit hard. Like 12k+ hard. For me it's vital on NM so I can take down Despair Demon with one mine (without barrier) which helps a lot here + dps from autottack isn't that bad really.
3. Virtuoso - offensive version using Power Chord. This spell scales great with crit damage.
On keeper hakkon is not needed, I prefer here dragon staff so I can use barrier and static cage ring and have HoK and fire source of damage. On necro it heavily depends on builds.
Walking bomb does not benefit much from Hakkon, only first hit can crit here. To use crit damage potential you need to use offensively Fade Cloak (the most damage on necro) or maybe energy barrage. Ice damage spells deal too less to be worth it.
On necro, with virulence passive, dragon staff and it's burning at the end of autoattack can add some aoe burning potential. Still it won't add huge damage, just help with tagging enemies.
As for the Razikale staff.
It's broken. Fade cloak blocks some abilities. You won't get barrier, you won't get healh/mana from death siphon. It's cool when you can use it on demands, but sucks as random thingy.