I received a teal Marvy LePen in my last Art Snacks box, and squirreled it away in my purse for later doodling and testing. I just rediscovered it among the gum wrappers and ancient Advil, and fished it out for a quick spin in the old sketchbook.
Because the LePen was included in an Art Snacks box, I'm going to review it as an art tool and not as a writing tool.
The LePen has many drawbacks which make it a less ideal inking choice out of available technical pens. It's very light weight, which is probably great for writing, but even with my small hands, I found it too light and thin to balance properly, and I had issues with gripping it. The LePen doesn't come with a marked size (it's probably only available in one), but I'd guess it's the same size as a .2 or .3 Copic Multiliner. Generally, the LePen feels cheap.
Inking with a LePen is similar in feel to inking with any non-art pen, so the results look very much like a doodle. The ink does go over waxy blue lines, which is a plus, and the ink is true to the plastic barrel color.
I do not recommend the LePen for drawing, but I'll probably keep it in my purse for jotting down notes or quick sketching.