There are quite a few cards that reduce cost for in-tribe cards - O Lórien!, King of Dale - to name a couple. I think this one absolutely knocks it out of the park for Creatures, so much so that I hardly use the readying unless I have a really huge Eagles of the Misty Mountains.
Reducing cost by 2 is already fantastic, and not even reducing with a minimum limit of 1 means you can play this and a Loyal Hound or something on turn 1. But I think the key part to highlight is just how good it is to play an Eagle ally 1-2 turns early. Everyone knows tactics is a slow, expensive sphere, and I believe the eagles have the impressive stats they do because of it. Their cost is also high to offset the benefit of their powerful abilities, needing you to hold on until they finally come in to save you (pretty thematic, I guess). Radagast's staff essentially negates these two drawbacks. Misty Mountain Eagles can come into play and start snowballing way earlier. Cards like Meneldor that you want to recur feel way better when that recurring cost is 1.
It is extremely powerful, and ridiculously fun.