I tried this on a light cream coloured carpet as one which might highlight best the cleaning power of this or otherwise. It is a carpet which tends to get a fair bit of muck on it from both human and cat occupants walking across it, as well as the occasional pile of cat sick.
The powder sprinkles out in very large lumps which bounce around on the carpet, and, as a result of Sod's Law, tend to bounce into the cracks between carpet and skirting board. The powder needs to be worked in with a brush, and again when you are doing this the lumps ping around all over the place and send yet more into crevices. I also got a lot of it trapped in the soles of my feet and ended up leaving lumps around the rest of the house as a result.
After all the effort involved in using this, the carpet was no cleaner than before. Looking at the powder in the vacuum cleaner, it looked just as white as when it came out of the packet. Speaking of which, a huge annoyance is that it seems to be completely impossible to reseal the bag after use. The instructions talk about folding up the bottom of the bag which has the sprinkling holes in it and then sealing it with the provided adhesive strip, but I was unable to create a seal which would stop powder still coming out everywhere.