Sparrow and Wren (ASUS ZenWatch 2) are rectangular watches. The two differ in size, wren being smaller, while sparrow is larger and adds a speaker. The ports are very complete and polished.
Sparrow and wren are rectangular watches with rounded corners and a power button on the right side. The display is a flat 1.63" OLED with 320px resolution on sparrow, and 1.45" OLED with a low 280px resolution on Wren. Both are protected by 2.5D curved Corning Gorilla Glass 3. Sparrow takes 22mm straps, while wren takes 18mm straps.
Repair and customisation
The back of the watches is held on by screws, so repairs are easy. Parts are commonly available. The display is usually shipped including the metal casing. You will likely need to replace the battery when buying these watches as they are getting quite old.
Miscellaneous hardware docs
Manually getting to fastboot
During the first seconds of the boot process, swipe diagonally across the screen. Starting from the top/left outer edge of the screen to the bottom/right.