This is an extruder design that is optimized for 3D printing or milling on a cnc mill. I've played with several of the existing extruder designs and found elements to dislike on all of them so far. Typically, you need to dismantle the entire extruder to perform the most mundane maintainence, which is crazy. I've played with the standard Mendel extruder, Wade's, and Makerbot Mk4. I've heard good things about the Paxtruder, so this design borrows heavily from that design(plastic pusher instead of roller) although here it's a PTFE button that is 3/8" dia and .230" LG. The material is available in 3/8" round and is soft enough to slice with an exacto blade. We turned ours down from some 5/8" PTFE round that we had laying around for making thermal insulators. It also uses the clever dual bolt-pattern of the Makerbot MK5 so that it can accept a gearhead DC motor or a stepper.
I don't have access to a lasercutter, so this extruder was designed to be milled or printed. The radii in the inside corners are to allow clearance for a 1/4" endmill. We printed a quickie today in anticipation of machining an aluminum one, and it works so well that we'll probably just keep using the printed one.
Ease of maintainence is key here. The motor comes out readily by removing 4 screws (multiple motor failures have made this an important feature at the Heatsync Labs hackerspace). The bore for the motor bearing is eliptical since the bearing only needs support opposite the pusher. This means that the motor/pinion/bearing can all drop out as a unit without disassembly and the extruder can remain mounted on the machine. This is an improvement over other designs that are a headache to maintain and usually require complete removal and/or disassembly of the extruder itself. Also the extruder body is extremely small, so it can be printed quickly and it fits easily into the machine. It's less than half the size of a Wade and probably only 70% of the size of a Mk4.