RedShark, in my own dim opinion, is a version of Apprentice modified specifically for the Pokemon TCG, available for download right here on Pokebeach. You can find out more about it and download it here if you want to: http://pokebeach.com/redshark
I haven't used Apprentice in forever, so I'm not sure if I can aptly compare the two. If memory serves, I don't recall Apprentice having the option to sort cards from the Deck Builder for Holon Phantoms on, which ensures that you only use legal cards, or automatically setting out prizes for you when the game starts. There's an icon next to the deck that displays a list of commonly used Trainer/Supporter cards when you click it, and selecting one will perform the selected Trainer/Supporter card's function, which is nifty. There's an option to restart if you have no basics, which automatically shuffles all cards in your hand and your prizes back into your deck and replaces them, also very nifty. The playmat shows the designated zones for your active/benched pokemon, Supporter and Stadium cards, and there are options that enable you to display an icon next to your card to show that it is affected by a special condition. And all things considered, the changes are so minor that if you've used Apprentice before, you'll find yourself right at home in no time. Honestly, I don't know why anyone would use Apprentice in its stead.