Been there with the brush tail thing for sure, it feels fine until the gray tells on you. A whisk gets everything smooth in like 20 seconds and you stop getting those little pockets of unmixed developer. I keep a tiny one in my kit now and my color comes out way more even.

Classic case of blaming everything but the real problem lol.

Ha, careful with that comparison though, coolant doesn't actually carry oxygen, it just moves heat away from the engine. Blood does both jobs at once. Cool analogy for customers but you dont wanna teach em something that falls apart if they think about it too hard.