I think it's pretty educational to watch. I think that the Leica he was working on was previously not tightened up. The screws and retaining rings look really loose (or he's really strong)!
So if you plan to open up your M, be careful as the screws are typically much tighter. The retainer under the rewind knob, in particular is something to watch for, as the notches are rather shallow, so if you use a screwdriver in that way, the chance of slippage is very high. A better tool would be a lens spanner with tips to fit.