The law covers indecent images of children. They must be engaged in, or appearing to suggest, a sexual act. Photos of naked kids are not illegal, otherwise every parent in the country would be on the sex offender's register. That photo of you in the tin bath when you were two will not get your mum in jail, nor the one when you ran around the garden in the buff because you didn't want to wear powder blue swim shorts.

The guy you reference was previously convicted of having images which were of children engaged in sexual acts. That is what he was originally convicted for. He was convicted the second time for having cartoons which were of the same type of indecent images of children he had previously been convicted for having. Clearly, this man has a sexual desire to (at least) see children engaged in sexual acts, and was therefore prosecuted.

Had the man not been convicted before of a similar offence, I'm fairly certain the outcome (and press coverage) would be considerably different.

Yes, the detonation can be faster than the speed of sound but the resulting sound only propagates at the speed of sound.

To get those bursts to propagate to the target at supersonic rates there would have to be combustible gas all the way from the device to the target.

A jet fighter going at mach 2 carries with it a sonic boom traveling at 6 times the speed of sound.
When it passes overhead at an altitude of 6k feet, you see it pass and you hear it 6 seconds later.
The sonic boom travels at mach 2 only because the fighter goes at mach 2, the sound propagates perpendicular to the fighter only at the speed of sound.

It is pretty impressive they can make a burst of sound move at six times the speed of sound.

Would it not just work as a Faraday cage?

Mobility
    What types of environment can they move about in? Desert? Shallow water? Everything in between?
    Are they small turtles or could the design be made self-righting?
Communication - Range? - Algorithm to leave a trail of relay bots for longer ranges?
Sensors
    Just touch? Basically just mapping then.
    Could they maybe have sensors for sniffing out explosives?
    Images? - Should a paranoid person worry if they find a few of those near a window?
Pollution - Do they contain heavy metals or other toxins?
Cost - When might these things be cost effective to deploy, say in Afghanistan?