I planted coated seed once.

Never, ever, ever again.

First, it runs through a drill like beer through a drunk. Expect a drill calibrated for, oh, 20 lbs/acre of uncoated seed to lay down about 27 to 28 lbs of coated seed per acre with the same setting.

Second, my soil had quite enough clay in it, thanks very much, and while I'm not an expert in soil science or agronomy, I reckoned that I had plenty enough clay and didn't need any more.

Lastly, you get much less actual seed in a 50 lb bag when 40% of the weight is clay. See the above point about having all the clay I needed.