The Tarantula's track system seems ... inappropriate. They're using wheels that will be riding on a rolled edge of the standard, aluminum 20x20 extrusion they're using. Compare to the Openbuild V-Slot extrusion which has a wider rolling surface.The FlyingBear looks better with more tried-and-true linear guide systems. It looks like it has a mechanical setup nearly identical to my FlashForge Dreamer (aka Dremel Idea Builder) which I'm sure was cloned from a Makerbot somethingorother. The first thing I'd do, however, is stiffen the sides; seems like pressure on any corner could knock the whole thing out of whack.Both seem to be using very standard RepRap electronics and firmware. I suppose that's not necessarily a positive or a negative. Not very refined but you can find replacement parts easily.On the whole what you're doing here is just buying "parts". I'd suggest you also take a look at the Monoprice line of printers; they don't have the 280mm build size but they're assembled and do get very good reviews.