I came across this the other day and thought if anyone else besides me takes these promises to plant trees or some other carbon capture method with a grain of salt.
As a search engine it acts as a proxy for Bing and then uses Open Street Maps when looking up addresses, so it adds a dash of privacy.
Its similar to those CO2 offset addons you can buy with Ryanair. The impact is probably low and fraud involved is likely high, but it is cheap and might be in the end better than a more expensive option that no-one uses/buys.