I hypothesize that consolidation rate/speed in the humerus matters far less than in the legs, tibias or femurs.

Weight bearing is essential so that you can walk. Not being able to walk is a huge hinderance. Luckily, with PRECICE nails, 50 lbs on the low end for each arm? You should be able to do just about any daily activity that you would do otherwise. Taking a shower, eating or drinking, driving, writing, typing, etc. Nothing is going to push the 50lb limit unless you are weightlifting or doing something very strenuous.

Information on humeral lengthening is a lot more limited, but I strongly doubt that getting humeral lengthening will even be close to the hindrance that is leg lengthening.