With Fortisphere having met its usefulness, discarding it to draw two cards was a popular play, meaning this one Steel item would give a Sapphire/Steel player three cards over the course of the game , and it was relatively cheap to do so
(Dont forget that you can use them to powerful effect with cards like Awakening or
Forrest Friend [US] (8/3/3), Gholdengo ex/Lunatone 170
If youre a new player looking to jump into Magic: The Gathering, theres no better place to start than Magics Foundations set
On the other hand, Theater of Horrors is generally a better Outpost Siege, since you have more time to play your exiled cards, though Siege does have the added flexibility of being able to be played as a win condition in Purphoros, God of the Forge decks and similar Go Wide decks