James Kyes: Yes, waxing will give faster skis if you have several pairs of differently ground skis to choose from, your skis are perfectly matched to your weight and technique, and your sponsors are willing to pay a really good waxer to prepare them for you while you sleep.
The context was recreational skiing and how to get fast skis without spending hours and hours testing and prepping.
Scraping has been extensively tested in here in Norway and especially in Sweden by many participants in e.g. Birkebeinerrennet and Vasaloppet. Many good skiers are very happy with their scraped skis, reporting new personal records and not seeing anybody with better glide during the whole race.
Con: Not as good as a perfectly selected, ground and waxed ski
Pro: Much, much less work, good glide that lasts the whole race (and a few hundred km afterwards).
These scrapers are razor sharp and ground in such a way that the edge is slightly serrated, which leaves a structure in the ski base similar to stone grinding, but (supposedly) smoother at the microscopic level. When completed with brushing and rilling, the result is so good that only elite skiers seem to be able to notice any difference.
My suggestion to a recreational skier who wants fast skis with the minimum amount of work would be to get three pairs, scrape them with either Kuzmin or Primateria scrapers, one each for cold, medium and warm conditions. Adjust with rilling as needed before the race.
Anyway, there's no harm in trying this out, if it doesn't work for you, just have the ski ground, sell the scraper and forget the whole thing.
Tip 1: I feel that the Kuzmin universal scraper works best between -2 and -8 degrees C, instead of the advertised +2 to -8.
Tip 2: Scrape off most of the ground structure with a sharp, sturdy knife before using the scraper. Kuzmin advertises that each of the four edges will be able to scrape five pairs of skis. I think two pairs is closer to the truth. The scrapers can't be re-ground, while a knife is easy to sharpen.
