Packing cubes become more useful when a suitcase is shared. The main benefit is not magic extra capacity; it is making separation, repacking and laundry decisions easier.
Check whether the set has enough different sizes for adult items, child items, toiletries and laundry. A cube that looks neat in photos can still waste space if the suitcase shape or packing style does not match.
Compression cubes need a separate check. They may help with soft clothing, but they can add zip strain and can make quick access harder.
Before buying, check dimensions, set contents, materials, zip layout, return terms and whether the current listing matches the route you are using.