A5 devices are also smaller. :P
That's really it. The PPI is also a bit higher since the screen is smaller but I mainly picked up the Note Air because it was half the cost of the Lumi. And well the case does look nicer.
There is another A4 device. There is the second gen of the Fujitsu Quaderno A4 that came out recently. Might be a bit hard to get though as I think it was only released in Japan. Here is a link to the new one on Rakuten.co.jp:
https://item.rakuten.co.jp/r-kojima/...1-a6e82e995bb9
The first gen was the same hardware as the Sony DPT but rebadged with Fujitsu software. Not sure exactly how the 2nd gen compares.
EDIT: Here's the official Fujitsu product page for the 2nd gen Quaderno:
https://www.fmworld.net/digital-paper/product.html