Just tried out Ogre Magi to see if the hero had any redeeming qualities. The answer: no, no it does not.
The problem is multicast, of course, but not because of the unpredictability. No, its because for whatever reason part of the skill scaling of Magi's three normal skills is built into multicast, which means prior to level 6 you've just got nothing. On paper two nukes with a disabling component should be great, the problem is that neither of their damage scaling is great, and while a 1.5 second stun is ok it doesn't scale at all from leveling. Bloodlust is probably the most useful out of the bunch but it has no real purpose in the laning phase. Its honestly at the point where if multicast wasn't a thing I would suggest putting one level into each and then leveling stats because the scaling is that bad. On top of that there's no good lane for poor Ogre Magi. As a laning support, your ability set is well suited to either commit to a kill or countering an enemy who commits, the problem is that your abilities are too mana-intensive to throw out for harass and you're a melee hero with low damage; so most of the time you're just standing around or denying which you aren't even good at. Offlane seems like on OK place for Ogre Magi but the short range and single target nature of its abilities is bad for flash farming and there's not much besides the hp pool to stop you getting zoned or killed. Mid is probably the best place for Ogre Magi, but... why would you waste mid on Ogre Magi?
Once you get multicasting up the problems mostly go away; the mediocre damage counts for a lot more when scaled up x2-4. Plus bloodlust can be applied to most of the team at the same time. But still, Ogre Magi outside the laning stage is just... mediocre. You've got a fairly mediocre skill combo you can use to gank a single target, you can apply weak buffs/debuffs to everyone on both teams, and you can spend 4k gold to get the game's latest developing stun combo online with unstable fireball, which will destroy your mana reserves if you ever use it. Bleh. The idea of a burst mage that just happens to have a bajillion health is great, but with weak escape options I wouldn't even describe ogre magi as particularly durable.