This topic is fairly old and has been inactive for over a year. But it still comes up in search. I am not a pro and have limited experience with Planex. I bought it in the spring of 2015 for my home remodeling project and used it with harness to sand ceiling at 3 stages of remodeling (3 different areas of the house), with a few months in between.
The first room felt like a nightmare, just as described in the opening post. The tool felt heavy and tough on hands and back. It was not a big room, but I barely made it through the ceiling. This did not sound right, and upon closer inspection, it was not. I looked at pictures and videos in the internet and realized that I did not set up my harness correctly (the pocket for the end of the extension tube was between my legs but should have been on the side of my body). The length of the extension was not set up correctly (too short) and the tool was too vertical. I also could not figure out the correct setting for suction, so I ended up pushing the tool against the ceiling. Any awkward movement would indeed lead to jamming the tool between the harness and the ceiling and scuff marks.
The second area was easier. It was larger, and I was less tired, and the finished surface quality got better.
The third area was yet easier. The tool still felt a little heavy, but much less so than in the second run and way less so than in the fist run. These three incidence of tool use were too far apart in time to call it "fitness level improvement". I think I finally figured out how to correctly set up the harness and the extension rod, how to set up suction and how to hold the tool correctly. It is right that with the right suction you can let your hands go and it will stay put on the ceiling. I found that the extension should be long enough to keep the tool at sufficient angle to the ceiling (not too vertical) and the auxiliary handle on the harness extension set should be high enough to control the tool easily. The tool should be moved side to side, not forward and back (this movement is done by your feet, not by hands). The third run ended with only one accidental scuff mark, much less dust than in the first runs because I did not need to detach the sanding head from the ceiling nearly as much, and much less overall physical effort.
The message is that this tool requires a learning experience to feel manageable. It is not a very long learning process, but it is not instant. On first run, it was hard, on the third sub-project it was even kind of fun to sand the drywall - quickly and without a dust mask and not nearly as physically heavy. My remodeling is almost over. I will most likely put the tool on sale some time soon as I do not anticipate its use in any near future, but I think I will be sort of missing it...
