Stratasys (redeye on demand) is a 3D printer. ProtoLabs isn't. The rapid 3-axis CNC machining ProtoLabs doesof simple small parts is exciting. I've used them to get parts. It can be a cost effective way to get reasonably simple small parts done quickly. Over time the types of things they offer (more threaded hole options, part size, maybe even 5 axis machining) should grow. The vendors in this space issue design guidelines / restrictions that are all closely the same for CNC machining. Suggests to me they all use the same machining centers - no real moat. Taking your drawing CAD files and generating the CNC programming is the tricky part I would assume but not something that others can't do. Similarly, the types of things that can be done by "printing" methods like Fused Deposition Modeling by outfits like Stratasys is growing too. They are a big player but have competition. Which has more potential, hard to say.