Interesting question. Do people still buy irons and iron clothing?

A clothing iron has a flat plate which heats up to moderate temperature, so I guess the question would be, what kind of situations would you need heat inputted in that manner?

Two come to mind, food preparation and plastics construction.

The first would be when you are making a larger meal on a more limited source, say like a stove with just a few burners and making multiple dishes. You might make a dish that takes less time, or needs to simmer. So a round thick metal or stone plate laid on top of the heating element of the iron (turned upside down) could provide a food warmer. Maybe incorporate it into a insulated container like a haybox.

The question then would be, what is the total energy use, and is it worth it to do it with an iron as opposed to other options. You'd need one of those meters to tell you what the electricity draw is.

The other is a more specialized use. I've often formed thin sheets plastic for craft project by laying the plastic on a cookie sheet, then setting it into an oven. I'd have to relook at the typical temperature, but if you heat plastic it becomes pliable and you can form it over a jig. Using your food oven for this though is questionable, lol, though I do it. Using a full size oven is probably energy intensive. Maybe a smaller over, built around an iron heating element might be more efficient.

For that matter, building a small scale oven, super insulated might be doable as well.

I use my iron regularly (a Rowenta with a big steam chamber).
Anyone who sews other than exclusively polar fleece uses an iron to shape, to press, to mold fabric so it behaves.
I iron facings and then sew them down so they don't have to be ironed anymore.

The leading cause of failure in irons is bad cats knocking them off the ironing board so don't just unplug your iron when you're done.
Unplug it and put it where the cat can't knock it to the floor.

... whether you kept food warm on a hotplate or an inverted clothes iron, the two should have exactly the same efficiency, because all of the electrical energy that they draw is converted to heat. In many applications, heat is an unwanted byproduct of something else: motion, sound, or light, but if what you WANT is heat, you only have two options: electrical resistance (oven, hotplate, magnetron, or iron), or heat-pump (which uses electricity to produce torque to produce motion to compress a gas "over here" giving up heat, and expanding "over there" to absorb heat). (Well, I guess I should mention solid-state thermoelectric heat pumps, but they're a niche.) The efficiency of resistance-heating processes just depends on how well the heat is concentrated on the food that you want to heat vs. escaping into the environment.