I am sure I am not the first but I just finished a bow and not wanting to clean up the sprayer I used a small 2" roller and rolled on the Thunderbird. I think I got a better finish than when I spray.
Ok
That might not be a bad way to fill and seal. I can see a lot of wet sanding to get a smooth finish though
I did use some 400 grit after the first coat and am surprised at how smooth it turned out. It is a fairly heavy finish and leveled out nicely .
I brushed it on a BBO once and it came out great. I ahold one run on the tip. That was easily fixed though.