Yes, they take off way more steel than other systems. Yes they will give your knife a 'stiletto heel' eventually because they dont reach all the way. Its even true that 'shaving' steel off against the grain like these do makes for a worse edge than doing it "properly".

However, my experience is that most home cooks walk into something like IKEA (excellent knives for the price btw) and buy knives in a price range where they would rather throw them out and buy new ones instead of having them sharpened. They dont want learn any method they consider tedious or difficult, and they dont feel like those knives are worth sending out to get sharpened. And if thats you, I think this might be the better choice.

If you have a high end knife or knives that you care about, I dont think this sharpener is for you. I think you are much better off learning whetstones or just paying a few bucks to have it properly sharpened by someone. But if the alternative is to throw it in the garbage when its dull, or just have the knife sit in a drawer without being used forever then yeah I would much rather see people use these than not.