@matigo The Nanos seemed like a hobby to me: the 1st one emphasised squareness: it was an angular rectangle with a square screen. The next one was almost the same but with rounded sides aka the old iPod Mini. Then came the "Chubby" 3rd gen with a 2-in rectangular screen across the top above the click-wheel. The 4th gen reverted to a long thin style with the same 2-in screen oriented vertically.
Gen 5 brought the most changes, it had a bigger screen (2.2-in), a VGA camera and a tiny speaker. To fit the bigger screen, the click-wheel was reduced in size.
Next was the more radical 6th gen, similar to the Shuffle, a square body with a big spring clip on the back and a square glass touchscreen. The speaker, microphone and camera were gone.
The 7th gen went to a rectangular form factor again, but with a 2.5-in glass touchscreen in portrait orientation. this picked up Bluetooth so it could connect to certain medical devices as well as for audio output. The 30-pin connector of previous Nano models was replaced by the Lightning port.