The idea is to use something 'starchy' to lightly scrub the surfaces and absorb old coffee oils. The urnex tabs are somekinda corn starch iirc.
I prefer cheapo porridge rolled oats to rice since they're a lot softer. You can see the old grinds being pushed out. Then a thorough vacuum. Mini has got an idiotic void in the upper burr carrier which stores a couple of grammes of old grounds and the only way to clear that is with a full stripdown.
One thing worries me about using compressed air -- could you be blasting dust down into the motor bearings and wirey bits? I've never taken mine apart far enough to see how well they're protected from the grinding chamber.