I will get used very fast to those arrows, I think. My previous phone, HP Pre 3, had a portrait keyboard and moving the cursor was done by holding down the symbol key on the *left* of the keyboard and swiping the gesture area. So...

I still vote for a portrait slider TOH, but if the keyboard's gonna look and work as awesome as the mockups, then I'd buy it in an instant and use it every day (IMHO it would be a nice compromise to the portrait slider I miss from the Pre 3 if it's gonna be this awesome as the mockups! )