How I do my BMF, cut and place on model, rub down on BMF with finger, use a cut down toothpick shaped to a flat-head-type shape and burnish that and then trim. After that I run a t-shirt or rag over the BMF to burnish it down more and sort-of polish it. I would be careful with the flux brush, you might scratch your paint or tear all the BMF off by accident..