I have a couple of rollfilm backs (6x6 and 6x7)that I use on my Tech V, and I find them very handy. I get the advantages of new formats without having to buy into another camera system, the convenience of rollfilm, and camera movements. Sometimes I may use sheet film for one purpose and then shoot rollfilm for another purpose (say B&W sheets and color or a higher speed film in 120), or I may use the rollfilm back when my longest lens isn't really long enough for 4x5". The rollfilm back is also handy for testing a new film or other piece of equipment or a new lighting setup, or when I'm just shooting casual snapshots that don't really need to be 4x5".
I've had a Graflex RH10 back and traded it when I got an older Linhof Super Rollex back. The Super Rollex backs with the lever wind (avoid the knob wind Rollex backs--frame spacing problems) are really well made, and the older ones with the tan leatherette aren't so costly.