Youd rather have Brazen Borrower against ramp, control, aggro, and midrange
After it has been paid, the auto-ability of the chosen effect goes onto the stack
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As with Energy Tap, the best way to get as much bang for your buck with an effect like this is to play creatures that have extremely high mana costs that become manageable to cast via cost reduction
So this being sorcery speed outside of blink decks does tend to limit it slightly, but even then its a powerful option to include
If you draft blue-green, look for creatures that would be powered up by receiving a size boost, such as smaller creatures with flying or trample