This is just as powerful as a modal spell, but arguably better since you can get both halves, not just the best one for that situation
A high-cost Character with 5|6 stats that can be used in slow decks, especially ramp ones, but he cant be inked, so thats a downside
You are never forced to activate mana abilities to pay costs, so if there is a mandatory additional mana cost (such as from Thalia, Guardian of Thraben), you can decline to activate mana abilities to pay for it and hence fail to cast the suspended card, leaving it in exile
If you're able to fill up your deck with cards that have additional triggers when they die, you can chain these abilities turn after turn to keep punishing your opponents until there's nothing left in play
I think of Ghalta when I think of 12 Mana