I have a set, and use them when needed, but take them off at other times. I also cut an old tyre's inner tube into squares to protect the roof/seam/channel area from scratches (I also space the attaching bolts with washers, because it turns out that they will screw in far enough to bottom out on the roof panel, gouging through the paint. Might not happen on any other brand of roof racks, but worth checking). The other reason I remove them when not needed, is that they tend to 'howl' with the wind whistling over them (or maybe over the ends of the horizontal bars.)

The ones I use are more accurately 'pack racks' - they have the two bars/4 legs like yours, but they are part of a larger frame with rungs - so more stuff (and odd sizes) can be fitted. I once carried 3 big screen tvs (old CRT style, not flatscreen!) on there to take to the recycling depot.