they don’t “plant trees” but rather contribute very little amounts to existing programmes

Ofcourse they don't plant trees themselves, it's a search engine with a small team. They donate their entire profit which averages upwards of a million euros every month, to local tree planting initiatives across the world and that isn't a 'little' number at all.

“Every search plants a tree” is a lie. It’s not every search, but rather every couple clicks on an ad

I agree, they were 'a bit' misleading with that in the past. Although they did state in their tree counter earlier and somewhere in their website/blog that it was roughly 45 searches (in Germany, depends on region) which raised enough money to plant a tree. They've since removed most, if not all of the misinformation.

They use Bing results making them useless

Since when does using Bing results make a search engine a 'scam'? DuckDuckGo also uses Bing results, would you call that a scam as well? Ecosia uses Bing search results because it's close to impossible to make an independent search engine which gives satisfactory results without the resources of a tech giant.