I'm sorry I just reread your post. You were asking about a walkbehind model. I used one for my dingo. I had a hard time keeping the unit level and no digging into the ground. When it did work it was fine. But I made my own coverup gizmo.
For smaller jobs or areas were larger equipment is not workable I have used a small 2 cycle garden cultivator. They are super lightweight and you basically just pull them back towards you it really works well and you can "flip" the thing to either side of the trench. I have watched the coverup video and it looked good but I wonder how effective it would be if the dirt was kind of spread out and smashed down?