Pokemon TCG Pocket is popular as it is free to play. Impatient players are willing to pay more to get cards faster.
Is it good? It depends what you mean by good. The game can be tough at the start if you don't have good cards and/or are new to trading card games. Compared to the regular Pokemon trading card game, there is a bit more coin flipping for attacks and mechanics. If the flips work for you good, if not then people get angry at the game.