There are now different kinds of cards split similar to these, and some of the rules have changed since the original question was asked
Lets look at Nahiris Molten Ambition by the numbers: 36 Equipment 28 Equipment @ 3mv or less 14 Living Weapons 5 Creatures that can tutor up Equipment or put it into play (Kassandra, Gilgamesh etc) 5 Early drop Creatures that reduce or free equip (Puresteel Paladin, Fervent Champion, Helitrooper etc) 31 Creatures (+4 if you factor in Pre-War Formalwear, Raven Clan War-Axe, Emerias Call and Inkmoth Nexus) 36 Lands (+ Land Tax, Sword of the Animist, Bitterthorn, Sword of Hearth and Home, & 2* Equipment Tutors) So, with 36 Equipment and 5 creatures that can find one, were at a whopping 96.9% to see two of them by Turn 3
You can't wait and use it to reroll that die later
These events require little to no cards to participate, and you get to open new packs and build decks on the spot
The grail card out of the Roaring Skies set values around $200 raw
This product does not contain a serialized card (available in English-language Collector Boosters only).