I've got one. Been doing some test prints with it with varying success. I have printed in Kevlar, but haven't gotten the carbon fiber yet. I was a little disappointed at how limited the options are with the Kevlar/fiber: you can choose either a concentric reinforcing ring, with an adjustable number of fibers, or an isotropic fill, where you can choose the angle of the fibers in each layer, allowing you to print adjacent layers at angles to each other for increased strength. Carbon fiber appears to be limited to the concentric option.

You can choose which layers to put fiber in, but you cannot choose specific areas of the layer. This means if you have a piece with a large cross section, but you only need to reinforce a specific part of it, you have to waste a lot of fiber reinforcing the entire cross section.

The fiber seems to extremely limited by geometry. You need at least about a square inch of area to be able to fit any isotropic fiber in the print. It will not be able to lay fiber in any areas of the layer that are much smaller. Concentric fill is even more picky. So far this has been the most frustrating limitation. If you print a plastic part with tabs that snap into another part, the printer will probably not be able to reinforce the tabs, which are the parts that most need reinforcement. You can't make small pins, rods, etc. out of fiber. Basically anything that isn't a relatively wide, flat sheet will not be able to make use of fiber. If anyone has found a solution to this, I would love to hear it.