Hi there, I have it. I have only just purchased the 10.1 2014, and it automatically did several updates when first using it. So it is running on Kit Kat. I can't compare to what it was before, because like I said, these updates occurred automatically. I have just downloaded an awesome camera app called Google camera, which works only kit kat apparently, and it's amazing.
I noticed that since the first update the notification bar has changed - it is smaller, but expandable.
I am still learning about the tablet and using it, having just sold my iPad, and I have to say - note 10.1 2014 edition is awesome.
I haven't noticed any downsides of it at all, but unfortunately, I cannot compare the android versions.