Well like I said above, you do not need to replace Android, you actually supplement it, its kinda linux on the go app. A lot of Pen Testers, will use this to quickly do a security test when they enter an organization. A lot of organizations do not ban phones in their sever rooms etc, so the Pen Tester can show why banning is a good idea. It is kinda like, always having your tools with you, just incase.
Apparently it runs really well, and isn't a memory hog. You can also concurrently switch back and forth, so say for example, you are hacking the server room from your Android, and your boss is like, what are you doing? You can simply exit out the app, and show im your text messages.
I think the most uses are for either security people, or their arch Nemesis, the humble hacker.
