Perhaps it’s common knowledge but I was surprised by this:

I bound Upheaval to level 1 Mogdrogen with 60 DA reduction
(also confirmed on Meteor devo later) 
I have 10% Crit Chance on a single Homestead dummy

I have 1 other WPS  25% chance Feral Hunger

devotion shows usual 20% chance for Upheaval to proc Mogdrogen
I expected the proccing to be very bad  20% on top of that 10% Crit chance is nothing,
similar to your usual WPS without many projectiles.
What happened instead was that I was able to proc Mogdrogen very quickly
after it cooled down with Upheaval, just as if it was a default attack replacer.
Turns out you don’t need to Crit and Upheaval to appear to attempt devo proc at all.
Instead of the proc change being
Crit Chance * (100%  total WPS%) * Devo Chance
and occurring only on Upheaval proc
(which would give me 10% x (100%  25%) x 20% = 1.5% proc chance
it’s (100%  total WPS%) * Devo Chance = (100%  25%) x 20% = 15%
so only slightly worse than Savagery itself (20%) in this case
(in comparison binding to Feral Hunger would give only 25% * 20% = 5% chance)
and you can proc devo with Upheaval even when Upheaval doesn’t proc
Of course other WPS don’t work like that and can only proc devotions when they proc themselves.
Perhaps it’s for balancing reasons because usually you have high total WPS chance
and you’d then never proc devotion with Upheaval if it needed criting as well
(well on a single target at least).
Another way to look at it is Upheaval proccing devo just as a typical WPS with (1  total WPS %) chance
which is on the level of other WPS if you have a few of them
but far better if you have only 1 like in my example (just Feral Hunger).