My machine has one. Push one button and it is threaded! LOVE it!!

I think it is needles with round eyes that don't thread. I love mine. It is wonderful. Just use needles with the elongated eye.

I received one as a gift from a fellow quilter and have yet to use it and I need to. Would save a lot of time threading needles.

I have one and it works about half the time. In other words, you often need to try two or three times to get the needle threaded. I can't remember which needles I've used it on, but probably sharps and betweens around size 11. It's a nifty little thing.