The Pentax 645NII is an amazing medium format camera and although it does look a little different, it does handle like a modern 35mm camera or any DSLR for that matter. Would you attempt to shoot handheld with 1/15s with a 45mm or even the 75mm lens? No problem! Follow the link for the photos on my blog that I have shot with this camera until now.
I do own the following lenses by now:
Pentax 645 FA 75mm f/2.8
Pentax 645 FA 45mm f/2.8
Pentax 645 A 200mm f/4
Like the Pentax MZ-S, the camera does record details of the exposure on the rim of the negative which I find helpful and which I usually add to the scanned image as EXIF data with help of EfixTool GUI. This sounds like a lot of trouble for little, but the EXIF data can be useful in Adobe Lightroom in smart collections when the number of photos in a catalogue grows.
The 6×4.5cm sized negatives are awesome and do give me the low-grain negatives that you would expect. I love to use this camera with the ADOX CHS ART 25 film for super low grain and loads of grey tones.