I have a little experience with the touch up pens, and I see them as a "tide over" until proper work can be done. First select the right one (matt won't work for a glossy finish blue and vice versa, of course). Then try a small dab on an area that isn't in view (such as under the foreend) by following the instructions (duh). Oftentimes results are marred by not degreasing, using too much, not rinsing and what have you. Let it dry properly and see whether it matches the surrounding area. If you are lucky, it'll match well enough for you to work on the visible area's - if not, don't try for the reasons above. Don't try it on anything too large to cover evenly - I have had good results on dings and scratches but I'd be hesitant to use one on anything bigger. Then again, if you consider reblueing the whole thing at some point anyway, you can try it out now without worry. But then there's the worry whether your new chokes will match