The ball mounts can get greasy or dirty and start to slip. If you clean them with alcohol it should help, if it becomes a real issue you can scuff up the surfaces for more friction. I use them for GPS mounting and my biggest annoyance used to be trying to get the mount back in the same position after taking it off. Adding a fine tip marker to my kit for marking the position solved that.
Some people have reported issues with those Rox Pivot Risers slipping which made me hesitant to use them on a different motorcycle, but I ended up running them for a while and they didn't slip. If you have any issues with them slipping, follow the motorcycle's service manual for the lower pivot. For the Honda Trail that means tightening the front-most bolts to spec (20 ft lbs) first, then the rear bolts leaving a gap facing the rider. Then do the same for the top pivot following Rox Speed FX's specs of 18-20 ft lbs, leaving the gap facing the rider. I think the issue is that since Rox Speed FX don't provide a tightening order people assume that as a two-piece clamp they should just tighten it evenly which is not the case for most bar clamps. I ended up replacing mine with bar back risers of similar geometry, less flex and look a little cleaner on the motorcycle.