I don't regret my purchase of the LoL starter set, but the online store within the game has a better option, IMO.
This card gives you Ashe, Ryze, Annie, Master Yi and Garren, a skin for Master Yi, plus a 7 day boost for XP (experience, which you gain by playing the game and is used to level your summoner up), and a 1-day boost for IP (influence points, or in-game currency you can only earn by playing the game, which you can use to buy champions. All-in-all a good introduction to League.
However, the game offers its own starter set in its online store for 530 RP (riot points, or in-game currency you purchase with real money) that features Master Yi, Warwick, Garen, Sivir, Ryze, Ashe, Annie and Nunu, plus a 10 win XP boost and a 7 win IP boost. The game gives you 300 free RP upon reaching level 3, and you can purchase 650 RP for $5, the same price as this card. Meaning that you could afford this pack, and at level 3 still have 420 RP left over, which is enough to buy another cheap champion, or a more expensive one on sale.
Ultimately, if you plan on binge-playing for a week, then the XP and IP boost might be worth more for you, as they're longer on the card. However, the online version provides a lot more characters, costs less, and will give you enough RP to fill in your stable of characters with something unique that looks interesting to you.