The Edelrid Ohm creates extra friction, allowing a much lighter belayer to belay a much heavier climber comfortably, without being pulled up to, or sometimes it may feel pulled through the first quickdraw.
I used this device on several occasions indoors and outdoors on sport routes (wouldn’t recommend using it on a trad route), putting it to the test. Where the belayer and climber have been of around 40Kg in weight difference (that is 6.3 stone), even two occasions where the climber has been up to 50Kg in weight difference (not recommended by the manufacturer, so please do not try this).
I obviously wanted to test it out. It is incredible. There is very little movement of the belayer, with a falling climber, on all occasions. From the small fall, to the great big wipper.
It is very easy to use. The climber attaches the Edelrid Ohm, loaded with the rope, to his/her harness, clips it on the first bolt, and just climbs as usual. There are no moving parts, and it is a very simple design, where the rope runs through the Ohm.