On the free plan a student can:

• create their own sets;
• practise them with flash cards and exercises;
• do assigned tasks and see their own results.

PRO adds what makes a word stick.

• Colour on the card. Mark the root, the stress, the ending that always catches you out — in
  twelve colours that stay readable on any screen. What you marked is yours to see everywhere the
  card is read, and never leaks into the answer you are asked for.
• Your own examples. Add the sentence you actually met the word in. A word remembered inside a
  phrase you recognise comes back faster than one remembered alone.
• Spaced repetition. The app brings a word back on the day you were about to forget it, and
  leaves alone the ones you know. It is in beta and open to everyone right now.

PRO can be bought from either of your accounts.