Form factor is super pocket-able and stealth, about 1.5" bigger in length than a Magic Marker and a tad fatter, but not the worst pocket bulk.
Also, its very quiet in the pocket because the pill shape cradles the marble.
Nib holds paint well depending on mix, but may not deliver the results you want after HEAVY use and ware. (a few inconsistent lines so i flipped the nib)
I did a fill with a couple Grog colours (70-80%) and Magic Ink White (aprox. 15-30%) its been a few weeks and the Magic isn't messing with the plastic.
(I forgot about the risks of Xylene (Magic) in the plastic body marker) but its super heavy duty and after several weeks is showing no sign of impact. However, i did a small qty. of Magic so don't try to come breakdown my boxes if putting Magic in the mix eats your marker.
Grab a pack of extra nibs while your at it, great for new color mixes, or crisping up those lines after prolonged usage.
I have three of these bad boys and with their quality build, they will be in the arsenal for ages.