Kevin, I have a 4x5 Shen Hao and I also have the 6x12cm Shen Hao roll film back. I use the 6x12 back a lot and have posted some example prints in the APUG gallery. I have had no problems with film flatness.
The Shen Hao camera has a Graflock type back, and the 6x12cm Shen Hao back has a matching Graflock interface.
You focus on the ground glass (also a Graflock module), then replace the ground glass with the 6x12 back, pull the dark slide on the back and take the picture.
The Shen Hao 6x12 back has a very simple design with a winding knob operated film transport. Film advance is strictly manual, you turn the knob and watch the numbers on the film's backing paper in a red window to maintain frame spacing.
Another advantage to using a 4x5 (as gilbeas mentioned) is that you can use 4x5 sheet film and crop to panoramic formats.
An additional 4x5 advantage is the wide availability of high quality wide and ultra-wide angle lenses for the 4x5. The Shen Hao will focus most WA lenses without a recessed lens board.