GMAT Strategy

I spend a lot time on the train to and from work. Can some one point me in the right direction for a good iPhone app (preferably free or cheap? Anyone else use these?

Here is my run down so far:
- Watermelon Express, pretty solid, but very buggy and expensive.
- There are a handful that just do flash cards, but lack any real explanation
- Knewton (or Exam Jam, I think) - Really strong videos, nice interface, it requires registration which is annoying, but hey its free
- Veritas seems more like a marketing tool than a resource.

What do you guys think? Have you tried any of these?

I agree with MDubbs.

Beat the GMAt flash cards are good
Exam Jam GMAT is solid - Knewton content... https://itunes.apple.com/hk/app/exam-jam ... 01319?mt=8

Any others