While you're totally correct - and these plug computer type systems do get used for penetration tests at least, it's important to realize that Eben et al. don't make the hardware or cause it to happen - the project is to about making a privacy enhancing distro to run on one.
> On a related note, consider the implications of someone dropping a box like this somewhere where there's open (say, municipal) Wi-Fi and 5 V from solar power or the mains to feed it.
Last year I did a talk at BlackHat EU on abusing MiFi hotspots to do this, only using the hotspot to attack the wifi network and tunnelling back over 3G to an out of band C2. I've got a lot further since then and have working PoCs that can do this.
They're ugly, but they work and work well.
I'm not sure it's a better solution for actual (black hat) hackers than paying for a VPS with a prepaid gift card or bitcoin (unless they need the webcam) but there's certainly some spy-movie appeal to it.