i have 2 models. the older sqare version and the half rounded lighter version they came out with. the rounded version is so light that if you dont put your full weight on it going from foot climber to the lounge itself it seems a little bit more prone to slide quicker. also when you lean to the left or to the right it shifts a tiny bit but nothing that feels unsafe. i did try using my square back bar on the rounded version and it seamed more solid. the other thing on the ronded version is when you done climbimg and sit in it its harder to push it full open than the square tube. all in all i havent had any problems with either model but i would get there latest square version if it were me.