Egg boiler. On the surface it's just the most gadgety pointless product invented but I literally wore it out because suddenly I could have hard boiled eggs and no risk of setting my apartment on fire because I forgot about the eggs. After I move, it's the first thing I'm getting for my kitchen because low-risk hard boiled eggs are totally worth it.

There's a lot of seemingly 'useless' kitchen gadgets like this: full size food processor, waffle maker, breadmaker, even my ridic large instapot. I don't use them every day or even every week and no, I don't need them for daily life. Yes I can mince fifty thousand vegetables for this really complicated soup by hand or make bread from scratch or do whatever you do to make a pot roast without them--but I won't do those things. I know me pretty well now; if I want to make that soup, make some fresh bread, or do that thirty-step fancy pot roast, I need those tools or I'll default to frozen pizza and maybe have fresh Italian bread if I went to Central Market recently and remembered to grab it from the bakery.