As a lefty, the ink's drying speed is key, but also, the size and shape of the nib. Lefties should be using big bulbous bold 1.0+ tip nibs that glide across the page instead of stab into it.

Unlike a rolling ball pen, it won't skip or fail to roll with pressure due to the rightward angle-of-attack against the paper, so a proper fountain pen is actually better than most other pens for us lefties. First time experiencing smooth writing in my life.

Ultimately, the enemy of lefties is the pointy tip, and the rolling ball that's expected to be rolled against the paper, not pushed against it. Felt-tip pens work just fine for us, so those pen Sharpies are alright, but so are the 1.0 bold tip roller ball pens from Pilot, at least all the Pilots I've tried. Can't say all the others work as well.