In Reno Mage, this is far superior to Chogall.
Mostly because you are not paying the health penalty (which is very relevant to Warlocks) and Mage has a ton of expensive spells they can use.
Pyroblast, Firelands Portal, Blizzard, Flamestrike, Cabalist's Tome etc. And now we have Kazakus potions too.
Chogall can be used in non Renolock and has better stats but that's really it. Warlock currently doesn't have the spells to support that effect but Mage does.
Easily the best Mage Legendary since classic although that still might not be enough if Reno Mage is not good going forward.
Also if it's not apparent, you need the spell to cost more than 3 for this to be worth it. Not that difficult to do but if you are using this to cast Ice Block then you are kinda wasting this card's potential.
the thing is many already try cho'gall in renolock, its total shite
Chogall sucks because it has anti synergy with itself and Warlock.
You want to play Chogall with an expensive spell.. but Warlock doesn't have many good expensive spells and even if you pull it off you are losing a ton of health doing it.
Wow... I just did Twisting Nether on turn 7 using Chogall and lost 8 HP. Sick combo bro!