Rubbing Down

The mouse is obviously a very useful tool for working in a lot of areas but still can't quite reach some of the more awkward nooks and crannies like the slim nose on the Powerfile which is especially useful for grinding off blobs of surplus weld and leaving a flatter finish.A very delicate touch is needed and don't grind off too much.
I use wire brushes of all sorts of shapes and sizes which are generally good for getting rid of surface rust etc., but still leaves the rough sort of rust-pitted finish you see on the swinging arm in the pics, which is where the Powerfile is so useful.
Having said all that and maybe sounding like someone who knows what he's talking about, in spite of all my efforts I still find it frustrating trying to get an nice even surface on the primed finish before applying the top coat!
Give up? Never!

I have ordered a flex shaft for my Dremel now, all other options see too pricey.

To get the very best finish you would use a high build primer and then wet and dry that to give a flat and smooth finish devoid of pits etc.
Finish the steel as best you can of course but to get the final high quality finish use paint as a filler, its far easier to flat than steel !