I am not familiar with the Gravity bicycle that you mention. However, I did buy a used Insight I this July and have ridden about 500 miles mostly on paved trails and some roads. I have added a rack and front bag and changed out the stock pedals for clipless. I was a bit nervous as some LBS people look down upon Diamondback but I've quite enjoyed it. I took it to the local Trek shop for a tune-up and the staff there didn't adjust the gears well so there is some clicking in high and low gears. But the bicycle itself has been a good purchase.