You can dump your mana into a foretell spell if you need to play a 1-mana removal spell on turn 3 but have nothing else going on
Mangara is certainly the stronger of the two cards, discouraging your opponents from attacking by granting you an extra card advantage if they attack with two or more creatures, or letting you draw a card when an opponent casts their second card each turn
The card is interesting because it will force you to build a deck a certain way to best utilize her, as lifelink can come in pretty handy to gain health
An effect that decks with commanders such as Queza, Augur of Agonies or Well of Lost Dreams may be very interested in
I loved this archetype when I played it in GP New York, but then I got complacent with it
In white, blinking permanents does the trick, while red gets impulse draw and exiles cards this way