I guess not if they're based in Estonia?
Aren't they sponging off the ill will created by somebody else?
If "Mango" can get away with it, I think it is very cool to provide a graceful path to open source tech.
I don't have much pity for the $33B company that promotes its mediocre semi-proprietary database to unsuspecting devs/students who don't know better.
But also I'm not lifting a finger to help companies like MongoDB, unless properly compensated.
Personally I hope that MongoDB does go for a trademark lawsuit, triggering the Streisand Effect. Then Mango can find a better name and attract attention.
The chance of them being successfully sued for this is ~100%.