The "when you play an Ally, something happens to your team" feels a lot like Slivers, as does the fact that our creatures can grow big super fast. Essentially, the way I view Red-White Allies is explosive and much more resilient, mixed with a more consistent (because we don't play all five colors).
Hada Freeblade and Kazandu Blademaster are the reasons to play an Ally deck in Modern. With enough tribal support, both of these cards are incredibly powerful, Hada Freeblade may look like a 0/1 on paper but he's usually a 4/5 by turn four, which makes him this weird, White "build your own Tarmogoyf" card. Kazandu Blademaster is really hard to deal with in combat thanks to first strike, and vigilance means he's always back on defense. Within a couple turns Kazandu Blademaster is usually a 5/5, which trumps every early game creature in the format.
Akoum Battlesinger and Reckless Bushwhacker, together, these two cards are the way our deck is able to win the game on turn four with some amount of consistency.
Picture this: we play a Hada Freeblade on turn one, a Kazandu Blademaster on turn two, and then a three-drop Ally like Kabira Evangel or Firemantle Mage (which we'll talk more about in a minute) on turn three. Our board is a 3/4 Hada Blademaster, a 3/3 Kazandu Blademaster, and a Firemantle Mage. On turn four, we can untap, play a Akoum Battlesinger giving both Hada Freeblade and Kazandu Blademaster another +1/+1 counter and pumping our entire team, then we surge a Reckless Bushwhacker to give our creatures another counter and pump our entire team two more times (once from Reckless Bushwhacker and again from Akoum Battlesinger). When the dust settles we have an 8/6 Hada Freeblade, an 8/5 Kazandu Blademaster, a 5/2 Firemantle Mage, a 4/1 Akoum Battlesinger, and a 3/1 Reckless Bushwhacker. That's 28 damage! Plus, all of our creatures have menace from Firemantle Mage, and if our three drop was Kabira Evangel instead, all our creatures would have protection from two colors of our choosing!
The other thing I love about Red-White Allies is we get access to the best reach in the format. We don't really need to get our opponent's life total to zero with our creatures. Instead we can focus on getting him or her to around six and burning our opponent out.
Lightning Bolt is simply the most efficient burn spell ever printed, and it was an obvious inclusion in the deck.
Lightning Helix is mostly a bad Lightning Bolt since it costs an additional mana, and our deck is fast enough that we don't care too much about the lifegain, but it can sometimes swing the math when we are racing against another aggressive deck.
Finally we have Boros Charm, which is usually a four damage burn spell that helps us finish off our opponent. Sometimes the card says, "You win a game you really, really should have lost," thanks to its ability to make all of our permanents indestructible. One of the things I dislike about playing aggressive decks is how they often scoop to sweepers ranging from Anger of the Gods to Supreme Verdict. Thanks to Boros Charm we have a main deck way to stop a wrath, which is never dead because we can throw it at our opponent's face. Oh, and don't forget Boros Charm has a third mode of giving a creature double strike. There are cases where we cast Boros Charm after blockers are declared on an unblocked Kazandu Blademaster or Hada Freeblade, and spot our opponent for eight to ten damage out of thin air.