In my experimenting to understand how much oil actually comes out of my 70's camshaft breather (prior to mounting Jim Schmidt's reed valve there) I swapped the rubber hose for a translucent hose. As you would expect oil was shot into the hose on the compression strokes. You could see a slow march of bubbles riding upward, thinning out as they went, then popping as they got too thin for the film to remain. When I turned the bike off they would all pop and run back down toward the camshaft port. If the port was closed, a surprising amount of oil would remain in the hose. (up to 3" ) One small bit of pressure on the kickstart would rotate the cam enough to open the port and the whole amount of oil would drain back into the cam.
This experiment was one of the reasons I route my breather back into the oil tank. With reed breathers, vs the timed breather port of the early model, oil doesn't so readily "drain back" into the crankcase because it can't get by the reed valve as easily as the timed port. I remember someone drilled a tiny hole below their reed valve to allow oil to drain back rather than remain in the hose.
I see lots of guys that say they have catch cans on their commando and it only ever has tiny amounts of oil in it. In my experience, I've witnessed enough oil exiting the breather that if I used a catch can, I would also pipe it's overflow back to the oil tank, just in case... Perhaps there's something different about the early model's timed port breather that makes it drink up more oil into it's port and expel it.
Pete as you already know, I've got 2 reed valves on my 70 model. The timing side blanking plate/mikes xs breather (like yours) and the Jim Schmidt timing port breather on the camshaft port. One on each side of the crankcase means that my bike isn't constantly pulling and pushing air back and forth between the timing case and the crankcase. Having run the stock camshaft rotating disc port alone, then in combination with the timing side blanking plate reed, and now a reed breather on both ports, I think the last version is the best. I think the second breather helps maximize the efficiency of both breathers by making a better seal on the camshaft port side. (Jim Schmidt actually did a video on that on youtube to compare the port output performance with, and without a reed installed. worth watching)
Sorry to be so long winded here,... the thing your reed breather will do is make it so your crankcase isn't heavily pressurized that you joints leak oil. The more efficiently you treat crankcase pressure, the less oil you'll leak. Your blanking plate breather looks just like mine, so I approve! If I was you, I would do what rivera did, put a tee in the 2 port hoses and route them back to the oil tank... Yes, that's what I did, so maybe there's some confirmation bias there... lol