Anki's implementation has some rough edges, but for $0/mon for multi-device use, it's an amazing way to get your feet wet with this learning technique.
$25 is surely expensive for a simple app, especially if you are a student without a steady income. But if anyone wonders whether Anki is worth this much money - try thinking of the potential benefits.
Why? Because it is the only way to support Anki's sole developer. He cannot take donations due to Japanese laws. AnkiDroid also does not take donations, though I do intend to start contributing code to that project.
If you really enjoy Anki, consider buying the iPhone app even if you don't have an iPhone.