I wouldn't waste my money on sedation free unless you are doing this for just asthetic reasons. But in order to clean under the gums which is what they need, they must have sedation.
If you have a grey savvy vet, you have nothing to worry about!
ETA: This is from Dr. Bill Feeman @ OSU:
As appealing as an “anesthetic free” dental may be, it may be a disservice to the patient. A complete oral examination or cleaning simply cannot be done in an awake animal, no matter how cooperative he/she is. Furthermore, the most significant tartar is not what you see grossly on the teeth, but what lies underneath the gingiva (gums). An anesthetic-free dental cleaning accomplishes little more than a cosmetic cleaning (like a teeth whitening procedure in a human) and leaves the most significant tartar and periodontal disease unaddressed. Not only may the cleaning not help the animal but it may fool the owner into believing that their animal’s oral health is being addressed, when in fact it is not. Please consult the following article for the American Veterinary Dental College’s position statement regarding anesthetic free dental cleanings: