I have been a Seeeduino fan ever sense I bought their mega board when it first came out. Seeeduino while fully compatible with the standard arduino, is certainly not a copy. There some really nice and useful features that they have added:
switch to enable/disable auto-reset
switch to manual select power source
switch to run board at 5v/3.3v
smaller usb connector
smaller external power connector
side mounted reset switch
optional shield connector holes at .1" spacing
So I say that Seeeduino took a proven open source design and improved on it.
Lefty