I've never tried brushing it on. It is certainly worth a try and you will know soon enough if it works for you.
The good news is that there is not much you can do that can't be easily corrected.
There are many ways to apply Tru Oil and you will find a system that works for you.
On smudging, a thin coat gets hard enough in about an hour to handle gently.
When wiping it on, I place / elevate the piece on a couple rolled up Tshirts and do the top and sides, wait an hour or so, then flip it and do the back. By the time the back is dry enough to handle, the top and sides are ready for another thin coat.
Here is a steel I recently finished up. The bulk of the grain fill was done by wet sanding a slurry with 400 and Tru Oil.
The bulk of the body was built up built up by wiping it on with a cotton swatch, (bulk 2x2 gun cleaning patches), and blocking out with 1000.
Once I got a good level body established, I sprayed 2 coats over 2 days and then left it to cure for 4 days.
The final process was to lightly wet sand with some 2000 and wipe one very thin top coat on, just enough to wet it.