I don't think they save space or make the initial packing any easier.
They don't save space because clothes are the same volume, plus the cubes themselves take up a bit more volume. They do not make packing any easier because you are still packing.
What they do is make unpacking and repacking easier. When we arrive, take the whole cube out and put in a drawer, try to generally keep it tidy, e.g. by placing laundered items back into the appropriate cube, and then when coming home or changing hotels, pick up the cube and drop straight into suitcase.
We pack mainly by type of item, so all underwear, all t-shirts etc. But we also do one big mixed cube with a bit of everything that we put in each other's suitcase on the way out in case of lost luggage. DH and I do our own packing and I much prefer packing his packing cube into my case than being handed a load of bits and bobs for me to find a spot for.
I know other peopleuse the cubes to pack day by day, but I cannot plan out my outfits on a day by day basis, so that is not for me.
A packing cube is a packing cube to me, I don't see how any could be more "good" than another.
