Thank you for your question. I contacted our fish team, and here's a message from one of our specialists:
The Matrix carbon is a chemical type filter media, that works to remove waste material from the water and polishes the water. Carbon filter media will need to be replaced regularly to optimize performance.
The Substrat Pro is a biological type filter media, that grows bacteria that consumes waste material from the water. Biological filter media is not designed to be replaced, as you will lose the accumulated bacteria grown on the media.
Depending on what filtration system this customer has will ultimately determine which media they should go with. Using carbon in a canister filter is perfectly fine, but it will need to be replaced more often, as it will be exhausted sooner. Biological media will never need to be replaced, but will need to be rinsed during water changes to make sure that large particles are not blocking the bacteria from receiving water flow.
There really is not an available comparison for these items, as they work completely different.