This is one of the best apps I've seen for studying GRE vocabulary but there are some issues.
Cons:
1) on some of the cards you cannot see the full text it cuts off half the text. Maybe this is fixed by purchasing it but I'm not willing to spend $2.99 to find out.
2) it's difficult to access words you've already mastered, are working on etc., I'd take some pointers from the Magoosh app (which is free by the way).
3) I'm not sure yet, because I can't access a master list of words, but it looks like the synonyms are not included as cards as well. I'm too afraid to say I know a card when I don't know one of the synonyms.
4) the cards appear to just run through a cycle and doesn't limit the number of cards you are trying to master at a time. So you run through the first 72 cards before it repeats....this is not an effective study method. It should be groups of about 15 cards and as you learn it the card is replaced with a new card to learn....and occasionally a known card is replaced back into the deck to check and make sure you know it.
Pros:
1) The biggest asset of this app is not only are the words a definitions provided with an example sentence, but they're are hints to remembering the words. I think this is very helpful and I have not seen it in any other app.
2) the actual "cards" are very user friendly. Easy to move forward, backward, and flip the cards over.