Like most Pokmon cards, the value of Pikachu ex depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Ascended Heroes)
They're powerful, flashy, and, for longtime fans of both games, pretty irresistible right now
Otherwise, it's likely to just run away with the game when your opponent untaps, and this is thanks to the fact that Urabrask is a powerful threat, mana roc, and board wipe all in one
Using Crispin you can quickly accelerate energy from your deck, making it much, much easier to get attacks off
That's a pretty good deal in our books, especially given the rate that modern Pokmon sets have tended to be snapped up and upsold