It's not clear, but does this app actually download the apks from the market?
I'm not as interested in the intended use of your app as I am the next obvious step, which is to have multiple versions of an apk downloaded and backed up as they come out. It doesn't happen TOO often, but it's clear that apps occasionally come out that break features, I'd love the idea of being able to roll back reliably at any time.
Phones: Nexus 4, HTC One, Blackberry Z10, iPhone 4
Tablets: Nexus 7, Samsung Galaxy Tab 10.1 7510, Blackberry Playbook
HTC Inspire 4g (Desire HD/Ace), HTC Raphael (AT&T Fuze),HTC Polaris (Touch Cruise),HTC Cingular 2125 (Tornado), Dell Axim x3, HP Jornada 548