Hi there, @Darryl 
Thanks a lot for the feedback!
You see, this feature is meant for the cases when you need to show the text in the results instead of the number (for example, calculate the T-Shire size based on the entered parameters (height, waist, etc).
Our users were asking for this feature and we’ve released it based on the comments from this thread.
However, I completely get your idea and agree that a field to apply a discount coupon would be just great. If your request gets more votes, we’ll try to think it over in the future updates 