That's massive potential card advantage in Commander
While you do have to flip a coin when its in play, its to stop it dealing damage to you
The possibilities for degenerate play lines here are endless: you can drop huge threats, funnel mana into win conditions like Helix Pinnacle, or just give your creatures pseudo-vigilance by using the ability post-combat
Nissa of Shadowed Boughs also gains loyalty as part of a landfall trigger, so its easy to cast it and get that downtick ability the same turn
You have to sacrifice those lands once theyve lost their counters, but access to a consistent proliferate source can keep them around forever, generating advantage every turn
You can include a lot of the same cards that you already have in this build, but youll probably want more creatures and fewer extra combat spells