I bought an air fryer a couple of years ago and barely touched it for months. Finally pulled it out of the cupboard again, and now I use it most evenings. Should probably have tried it more than twice before deciding I’d wasted my money.
My noise-cancelling headphones were another one. Felt like too much to spend on headphones at the time. I wear them on my commute every day now.
I had the same doubts about our robot vacuum. We already had a regular vacuum, so buying another thing to clean the floors felt unnecessary. Now it runs most days, and I’ve got used to coming home to floors that don’t need vacuuming.

What have you bought that you initially regretted spending money on and then ended up using all the time?