I have an inline oiler sitting on the shelf. It was too much of a mess to be worth the time and effort. It also slimes the inside of your air hoses over time and causes deterioration.
I oil my tools before I use them and again when I put them away for the day. On stationary air tools, like my planishing hammer, I installed a small inline oiler a few feet before the tool. I used a standard 3 foot section of hose to plumb the oiler into the tool.