Features or more functionality in a product is what a customer want?

[Customer experience]

I have started a hardware startup with one of my techie friend. Couple of days back we had an argument over adding two or more functionality or feature in our product.

As a user experience designer I always think that customer doesn't want something which has a lot of functionality or features in single product. I always think that adding more feature neither full fills the customers' needs or business requirement.

His argument: What if some company started selling a device which can two jobs - for example: Imagine there is a device which can take temperature and blood pressure both with just one device, wouldn't it make device more sell-able? Combining two different device into one can cut the cost and provide two solution almost as the price of one.

My argument: I said," would you buy a home appliance which can do more than one job." (He said yes) Then I gave him one example - what if there is a device which will have microwave oven + washing machine, would this make device more sell-able?

Later, I realize that my example has two devices from two different domains where as his example had two device from one domain so I changed my example to this - Imagine there is device which can work as juicer + microwave oven would you buy it?

I wasn't able to convince him that the approach he is taking is wrong and I am fairly confident about my approach.

I would like to take some comments about

  1. If I am really correct or wrong then why?
  2. If he is correct or wrong then why?
  3. If I am correct then how should I approach to make him realize that his approach is wrong.

Please let me know if you want any edit or more information.