Besides a dice that's as even as possible, the other requirement this solution attempts to satisfy is using the minimum number of cuts. A blender doesn't satisfy that, as it's making hundreds of cuts.
Then, when you present your solution to the client, you find out there was a third, unspoken requirement: that it should involve as little cleanup as possible, which the blender also doesn't satisfy. The user researcher was on vacation, and you didn't find out about this before beginning design. Damn!
The blender solution turns out to be overoptimized on a single requirement at the expense of the others.
They're optimizing for time as knife cuts = time. A food processor will do it faster if you're more than one onion or so, assuming you can get the size you want.
Ahh, so in addition to having trouble getting consistently-sized pieces the size of a dice or chop, the other reason knives are preferred is that a food processor damages the onion, releasing more water compared to a knife. The result doesn't caramelize as well. This is why higher-end restaurants cut onions by hand, even when operating at scale.
Anecdotally I've prepared caramelized onions both ways, chopped with a knife and using a food processor and I've never noticed a difference. Onions have to release most of their water before they can begin caramelizing anyway so if anything, wouldn't that speed up the process?
You don't have to turn it into mush with a food processor, not all veggies are caramelized. High end restaurants usually optimize for speed but not over quality. Not sure why were talking that when this technique is for home chefs.
A blender will make the bottom layer into paste before the top is touched. If you want to toss the paste into a skillet and caramelize it, that'll make a good sauce.
Food processor might be better, but still won't be even.
Source: I cook onions a lot, and am lazy. This article is great!
Always bust out the food processor when making soffritto or similar very small dice. Can do onions quickly and even with the method but carrots and others take quite some time.
I don't think this gets you the texture you're looking, or even cuts. My eyes are tearing up right now thinking about scooping this out of the blender.
Spice blenders tend to have blades closer to the bottom and are fine for dry things. Still not good for dicing though, especially as onions aren't really dry but full of liquid.
