I think that regens are useful for almost all heros in the early game, this makes the tiamat a good way to save gold in the game, you build the tiamat from 4 fairly inexpensive items making it a very incremental item to build. It gives a solid 42 damage, splash and both regens. While it gives an insignificant 4 mana regen /5 , the 15 hp regen / 5 helps any hero stay on the front for longer than they would be able to normally. OK, so its not the BF sword, you know what tho, for 8 less damage and the added regens and stack, it is a very worthwhile item to build.

I can't say that I've seen a good use of Tiamat. I'd like to buy the item, but I can't justify it.

Maybe if another combination stepped into it. Like Perseverance did into Battlefury.

I've used it on Teemo in a 1v1 match. It was fine, but I would probably not get it again.

Sunfire cape<Tiamat.

Stack'em and watch the enemy burn. With enough life to do so too.