How does it counter the summoning? Are you casting it on their new summoned creature to teleport it away from defenses and into range of your most powerful attacks? Or just away from you? It only seems a small tempo advantage for 10+ mana?
PS steelclaw, is Samandriel that bad/different? It essentially comes with built in bear strength and divine might, so same casting cost as angel plus these. Sure you can't Et them, but they can't be dispelled either and there is tempo advantage. Although perhaps not that great with your stack approach. The SB cost is probably the main sticking point I guess.
If you reveal the DI and move the opposing mage to another zone
before the creature spell resolves the spell will eventually fizzle because the mage is no longer in the zone which he originally targeted when casting the creature spell. ( range for a creature is 0-0 )
Samandriel is not so good in "taking care of herself" as the Guardian Angels.
She has no built-in defense and cannot heal herself.
She costs almost twice the price of an Angel and weighs in at 5 sbp's.
I don't mind losing an Angel, so I don't have to go out of my way to protect them
whereas Samandriel is such an investment you have to account for her safety all the time.
Therefore I prefer 2 Angels over Samandriel.