It’s probably only worth using ecosia if you think your time is virtually worthless. Tree planting is mostly a useless activity in the grand scheme of things, though one gets into a somewhat complicated calculation to show this.
Google claims there are 3*10^12 trees in the world, ecosia claims to have planted about 10^8. Trees are in an equilibrium with a bunch of stuff like atmospheric CO2 as well. Your personal contribution to the number of trees via ecosia is likely ~ a few trees (not clear whether they reach maturity though).
Do anything else useful with your time before this.
On the effectiveness of treeplanting: Would you mind linking to those calculations? Trees remove ~130 giga ton CO2 annually and with your number ecosias trees remove ~4*10^6 tonnes CO2 which is something like 10% of the worlds annual CO2 emission from fossile fuel. Granted, its a lot more complicated and it obviously isn’t a feasible permanent solution given saturation and whatnot but it seems like an intuitive delaying measure, at least insofar as their forests take a good while to reach maturations.
On Ecosia: Their April financial statement says they spend 14% of their income on green investment so it’s not exclusively treeplanting.