You can change the quality on the video from compressed to original in the video play settings itself and then just download it using add-ons like video downloadhelper or IDM or something else. When you change the quality you should see the larger version available to be chosen. Of course you have to have access to the video (free or purchased) to be able to grab it.
Then I am at a loss. I just went out there in Chrome and selected free and the first video that was in the list had no Quality option to change but the second one did. So I have no idea why you wouldn't have that wheel like button show up to change the quality on videos that have both a original and compressed version available to play. I am really not sure what could be stopping it from displaying on the player.
You know what, I did some more checking and I am noticing the same thing. This is new. I even checked one that I "made a local back of" a few weeks ago. It is the correct size that the video states it should be at 645MB but is not the size that IDM shows available to grab 396MB, which would be the compressed version. Interesting, I wonder if they decided to only offer compressed for streaming only now.