I think that indeed this interface is more "natural" for those of us who do not use calculators all day and every day. Practitioners have presumably already made the necessary learning to adapt to the calculator interface. For more infrequent users (e.g. me), this new interface would really help - and it ties right back into how I learned mathematics with pen and paper.
A good interface should disappear when you're using it - it should never, ever, get in the way. That's one of the reasons why I hated with a passion the old Reverse Polish interfaces on the original HP calculators, and why I still end up with wrong answers on today's calculators - the interface is fighting with what I learned with pen and paper.
I've downloaded the software, and am trying it out on my PC, which has a graphics tablet. If this works, then I'll be able to consign the Windows Calculator application to the dustbin of history...
P.S. I simply adore the title of the web page at the University of Swansea.