The sales representative demonstrated an..........labor-saving device.
Interesting or interestingly
I think ( interestingly ) is the answer because it is an adverb that describes the adjective( labor -saving)
I think only "interesting" works there, because "labor-saving" typifies the noun "device" and forms a unit with it. Also, the adjective is not gradable — we cannot say that the device is labor-saving to an interesting degree. We are speaking about a labor-saving device that is interesting.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .