I wonder what kind of placement accuracy that arm gets, both relative and absolute? Seems like that arm is doing better than I would expect for the size/weight of the actuators. Not something you'd be able to do without an extremely expensive arm.
to me, the big benefit of something like this is that you could reasonably run 7axis - Arm is 5 axis, but then add tilt/swivel to the bed. it would allow you to choose in which direction you were building. I don't think any of the standard slicers for cheap 3d printers can do that stuff yet, but maybe eventually CAM packages will be able to support more modes of additive manufacture.
that said, for large parts this would maybe be worthwhile. For smaller complex parts, the powder bed approach for the HP multi jet fusion printers (an example) is still nicer than this because it keeps the part fully supported during the whole print so you don't need to worry about slump.