So this is a tricky question. Because… There are actually 3 versions out there now.
First batch of MK1 also had a accelerometer built in. So you could physicaly do acrobatics with the unit and that would do something inside the UI. Novel idea. This was ditched after the first batch.
So a year later MK2 came along. Which is a cosmetical update.
I believe the touchpad is not bigger, but only recessed. They did it for a “better feeling” where the touchpad is without having to look at it. And yes, MK2 has a plastic screen protector, new housing and new text prints. But internally it is 100% the same.
So any actual internal differences are between the first batch (with the accelerometer) and all the rest. But first batch and all other MKI are 100% the same from the outside. And MK2 is just a cosmetic upgrade.
All in all there is literally no difference. Just get one.