You're limited to how many of each pack you can buy by your DP (Duel Points, this game's currency) and by the limit Grandpa (the shop owner) puts for each pack
Prices for Skithiryx, the Blight Dragon and Elesh Norn, Grand Cenobite, for instance, have both fallen by around $25
They sell the pre-packaged ones created and distributed by WotC, and complete decklists that are built by expert Magic players. This is an attractive choice for anyone who wants to avoid building their own deck but isnt a fan of the ones you can find at Target
It provides protection against anything your opponent throws at your monsters, barring battle destruction (which you can deal with using the Field Spell and/or Genesis)
If an opponent has multiple votes, it's possible for them to count as both an opponent who voted for a choice you voted for and an opponent who voted for a choice you didn't vote for
To use these booster cards, all you need is a 60-card playing deck