As somewhat of a sympathizer of effective altruism (the idea of efficiency being an important factor in charities, not necessarily the implementation and even less the community), this isn't super appealing to me.
Who doesn't? Why else would one make money other than to do something with it?
If they didn't make money, how would they support the tree-planting?
This just seems like a donation with complicated extra steps, in the same way that e.g. "rounding up to charity" or even "round up savings" do not appeal to me at all.
That might well be an idiosyncratic preference, and to some the idea of "planting trees via running web searches" might appeal much more than a nonprofit search engine that donates to a basket of charities, or one that directly pays the user for showing them ads and lets them decide what to do with the money and then the user donating the proceeds themselves.
They are very transparent about it. They list the amounts paid, the partners, the tree species, etc.
They are also fairly efficient from what you can tell by their reports.