The single roller design of the 910 is a weakness of this design but it just is a matter of degree. It's hard to find dual wheel machines under $1000 due to production cost.
I have often mused about dual wheel front drive machines vs single wheel front drive machine. The dual wheel versions just hold up better due to better weight distribution on the wheels. It's a simple issue with the amount of force per pound per square inch on the wheels. It's magnified with front drive machines because the entire user's weight is on the wheels. Wheel systems that are on rear drive machines don't have this problem because of the distribution of the weight onto the rear drive mechanism.