This is the most camera you can get for your buck feature-wise. It's a lot larger than other mirrorless cameras, but the major advantage is that it takes standard K-Mount lenses and only has a 1.5x crop. You really can't beat that crop on a mirrorless camera.
I'm curious how well the screen works for manual focusing. I'm a long time Pentax user and have a pretty great collection of older K-Mount and screwmount lenses that I use with an adapter.
You get the same crop on a NEX. The big problem about the K-01 versus the NEX is that you will be limited in the amount of legacy glass you can use. The NEX has a super short registration distance so pretty much every piece of glass ever made will work on it. The K-01 has a much longer registration distance. But if all you want to do is use PK or M42 glass, the K-01 is an awesome camera.