I've tried some mobipocket books after firmware update ( thank you, cbell, for pointing out they are now supported) and I really like the way they look on V5. Again, there are extra menu options ( although some of them are a bit redundant) and internal hyprelinks work really well.
@Suzannec - ECO reader is a bit bigger and a bit wider than Hanlin V5. If you go
here, you can see by how much they differ in size/weight.