How do you correctly soften butter for spreading?
If you want to turn your cold butter spreadable quickly, patience is about your only option. You can try microwaving it very briefly, and maybe on the "defrost" setting, but you run a strong risk of melting it too much.

If I'm thinking of the same thing you are, a butter conditioner is really just a unit that allows you to keep your butter in the fridge but still keep it closer to room temp--so that's more about storage than turning hard butter into spreadable butter on the spot.

A storage option that allows you to keep your butter fresh for a pretty long period, but still leave it out on the counter so it's soft, is a butter bell. You can look them up online--many shops have them. It's basically an inverted cup that sits inside a larger one with a little water at the bottom. The butter is packed into the inverted cup and stays put when you place the cup so the edges are under the water in the other cup. The water keeps air out so the butter stays fresh even at room temperature. You could do the same thing by mashing a bunch of butter into a teacup, then setting it upside down in a saucer full of water. If it's too hot in your house, though, the butter will slip out of the inverted cup, so I mostly only use our butter bell in the winter.

One thing to note about butter itself: Some butters are more spreadable at cooler temperatures. The Irish and French butters we can get here are much closer to spreadable at refrigerator temperatures than the regular US supermarket brands. I'm not sure what the difference is, though.