Can someone please explain Amazon Instant Video for this situation?

[Celeriacacaca]

I want to buy a series for DS and download it (as oppose to stream) it onto his iPad. Should I do this via Amazon Instant Video or is there a better way of doing it? TIA.

I can't work out how to download to iPad using Amazon Instant Video. It only streams. Is downloading even an option?

Newest version of Blinkbox app I think allows downloads but I have not yet tested that.

iTunes?