In my experience, hand-whisked mayonnaise is a bit “loose”, as people say.  Blender mayonnaise is thicker but troublesome.  I much prefer to make mine in the food processor; the resulting mayonnaise is very stiff and very unlikely to separate, and the processor is much easier to deal with than a blender.  The drawback is that you really have to make 2 cups in the processor—any less, and there isn’t enough egg at the beginning to come to the top of the blades.

I don’t use any kind of drip mechanism.  I just pour the oil very slowly at first, just a glug, and then another glug, gradually moving on to a thin, steady stream.

One thing I learned the hard way is that canola oil doesn’t work well at all.  I hate canola oil—it’s thin and gritty, like mineral oil, it has a sour taste, and it breaks down at low temperatures, filling the air with a fowl odor—but for some reason, I had to use it once, and the mayonnaise would not thicken.  It was thin and nasty.  My preferred oil is peanut oil, which I use for everything, not just mayonnaise.

If you want olive-oil mayonnaise, beware of using 100% olive oil in the mix.  The flavor is overwhelming.  Even half olive oil might be too strong for some, but you need at least one-fourth olive oil to get the flavor.

The food guy, Kenji López-Alt, makes mayonnaise with a plunge blender.  I’ve tried it and it works, but I prefer the food processor.

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I’ll add that I don’t make my own mayonnaise for everyday use, but I always make it for potato salad and deviled eggs.  The egg flavor of homemade mayonnaise really comes out in recipes like that.

As for cost, though, I would not say that my homemade is cheaper, since I use peanut oil.  But for the flavor, when you really want or need it, homemade is the best.

One of the features of the early Cuisinart Food Processors was a tiny hole at the bottom of the opaque plastic pusher for the feed tube. It was to drizzle oil into the egg yokes while making mayonnaise.