Product Design - What is the killer feature?

Recently I bought a Warm mist humidifier for my home. The product works great and this blog post is not a review of the product. I will try to put myself into the shoes of the product manager for this product. When the product was under design, the product manager and the engineering teams studied competing products and listed certain features that the competition has: 

1. Support for adding the inhaler or cough suppressant
2. Auto shutoff when it runs out of water
3. Should last 8 hours

In addition they must have considered the pricing to make sure that it is few dollars cheaper than the competition. I am guessing under the competition and market pressure what they forgot to do was add an on/off switch to the product :)

The product does auto-shutoff when it runs out of water but to turn it on again (when I fill the water), I need to pull out the plug and put it back. 

Interesting learning for me as a product manager: Create a list of basic features that a customer cannot live without in addition to studying the competition. Assign weights to each feature in the list so that you don't ignore the basic features.