Making it is easy, but we don’t use much and the shop stuff seems to last forever, home made not so confident once its been in the fridge a while. I suppose that is maybe another reason to make your own.
You also use less when you make your own because you become acutely aware that it is almost entirely oil.
I just put the approximate amounts of egg yolk, mustard, lemon juice or cider vinegar and oil in the blender beaker, then blend keeping the blade right at the bottom of the beaker until everything has emulsified, if its too runny add more oil and go again