Because I failed at homework and only found out it exists after having ordered the sonnet :/ EDIT: It was a good move. TH05 = ONE thunderbolt channel. 10Gbit/sec in each direction. Equivalent to two PCIe 2.0 lanes electrically. (PCIe 2.0 = 500Megabyte/sec per lane) Sonnet Echo Express Pro: TWO thunderbolt channels. 2 x 10Gbit/sec in each direction. Equivalent to four PCIe 2.0 lanes electrically. This is basically the same bandwidth good'ol AGPx8 (or PCIe 1.0 x8) used to give us. See here: http://store1.sonnettech.com/product_info.php?&products_id=403 Unlike its 2011 sibling, the 2012 macbook air has a dual-channel thunderbolt controller. The sonnet takes advantage of it, doubling what is effectively the biggest bottleneck in the system - the interconnect between the CPU and GPU.