The dimensions are odd - not enough in one dimension and too much in another. At 35.8cm wide, it's less than most airlines' 40cm maximum width, so it doesn't maximise potential internal space. And its depth of 22.9cm is too deep for the likes of Ryanair.
Most US airlines cap it at 36cm which is why this one's at 35.8cm. Yes Ryanair caps depth at 20cm though I would say they are the exception as most other international airlines are OK up to 23cm.
I would like to see a built-in Li-ion battery that cannot be quickly removed without tools, so that airlines cannot choose to gate-check it, but cannot deny it entry to the cabin.
Interesting you say that as I thought having a non-removable battery (or a battery at all for that matter) would be seen as a big no-no. Personal preference I guess.