So, I decided to try out the pens, and I love them!! I think my frustration with small brushes is the bristles sometimes go every which way, or split ever so slightly. These apply the dye in a similar way as spot tone with a 000 brush, but having a pen tip has been very helpful for me!! And I'm not guessing at how deep the tone is... in other words, I don't really need an extra paper towel to assess how dark the dye is. It's pretty clearly marked on each pen.
Thanks to everyone for your thoughts on these. YMMV, of course, but I think I'm going to turn to these pens more frequently than the brush from now on!!!