Nice review!
It looks like a wonderfully nice toy, it's on my wish list too for some while, for when my HW dies or Pi Zero will be again in stock in my country, whichever comes first.
Until then the software should also get more mature + maybe Electrum will also implement the missing feature(s).
I'm assuming the dearest piece of kit here is the camera, which might not be necessary for users that don't want to scan QR codes? Since, most other hardware wallets don't offer this, you could potentially even argue that this is an additional expense that isn't really needed. I guess the convenience is there if you need it though.
Camera + screen are the two directions/devices for transferring information between SeedSigner and the hot wallet. Both are crucially important.