What you need to ask really depends upon what you want to know about the product.
This may not be what you're looking for but the SUS (System Usability Scale) might be a useful alternative.
The NPS is a very easy scale to administer which is an advantage over the SUS's 10 questions but this means it is a more subtle measure because it measures more than one thing. Commonly, an overall SUS scale is reported – in my experience, it's easily understood, but can miss some of the subtleties.
If you need to stick to a single-item scale, then one of the SUS questions might be an alternative. Question 9 ("I felt very confident using the service") seems useful.
- I think that I would like to use this service frequently
- I found the service unnecessarily complex
- I thought the service was easy to use
- I think that I would need the support of a technical person to be able to use this service
- I found the various functions in the service were well integrated
- I thought there was too much inconsistency with this service
- I would imagine that most people would learn to use this service very quickly
- I found the service very cumbersome to use
- I felt very confident using the service
- I needed to learn a lot of things before I could get going with this service