Of course, you have to pay for the cards, but the possibility of playing Magic anytime you want compensate any financial problems.
I have been playing this since 2000, and I have never had any problems yet, in fact, I judge their security and stability to be a good side of the program.
Besides the online quality, the game is perfect. It stops at every step, you can respond to any spell your opponent casts and even teaches you how to play the game! It´s really a wonder!
Daily championships and draft every hour makes the pro player rejoice and learn about the metagame faster. Sealed and league complement the championship part of the game.
All in all, a true masterpiece. A game to play forever!