(Susan M. Pigott is a fountain pen collector, pen and paperholic, photographer, and professor. You can find more from Susan on her blog Scribalishess.)
Out of the wilderness between the mechanical pencil and the lead holder, comes the Kokuyo Enpitsu 1.3 mm mechanical pencil. It was designed to mimic the simplicity of a wooden pencil, but with the convenience of a mechanical. It does achieve this goal, though obviously not without sacrificing some features of both.
The body is fully coated in a soft rubber, which makes it very comfortable to hold, even for long periods of time. It has a very slight triangular shape--just enough to keep it from rolling on a flat surface, but isn't in any way intrusive to how you'd hold the pencil. The lead and metal nose retract completely, so there's no risk of lead marks or breakage in a bag or pocket. The lead feeds in through a hole in the top of the click button. It has the potential to fall back out this way, but it doesn't happen easily. Since I didn't have refills handy, I'm not sure how many pieces of lead it can hold at once, but it doesn't look like there's room for a lot of backup--just the one in use and a spare. And that's really it--there are no removable parts, no eraser, no clip--it really is a cross between a wood pencil and a lead holder.