Pros: Easy to use, inexpensive, good results
Cons: Must "re-angle" cutting edge, does damage blade
I've only sharpened a couple of knives with this sharpener thus far, but have been satisfied with the results. I have a block set of inexpensive knives that never have been sharp enough. This particular knife design has a wider edge at the back of the heel, which doesn't work well with this sharpener, but I am able to sharpen all but the last inch or so near the heel. With knives that don't have this sort of "flare" at the heel, the full knife can be sharpened with ease.
Because this device uses a standardized angle to help make the sharpening more "foolproof", you must make the edge fit the angle of the sharpener. The first sharpening on each knife will take longer than subsequent sharpenings.
I have read several reviews which caution not to use on expensive knives, and I think that's fair. Since my most expensive single knife is about $30, I'm not overly concerned with wrecking the knife. I had a 12" or 14" chef's knife that I purchased at auction that simply never had a good edge on it, even when new. I now can shave hair off my arm (old redneck method of checking sharpness). I did find that my handheld chef's choice sharpener (about $10) works better on the stage 2 portion. The electric version might be better once I get more used to it.
I did cause a few errant marks on the knife by inserting it into the sharpener in a non-perfect manner, but these were cosmetic scratches.
There is certainly room for improvement in this device, but it's $29, so I have to factor price into the equation. The magnets could be much stronger to force better compliance with the angle of insertion. A third-stage of even finer honing is available in other sharpeners from this company, and I can see where it would be a welcome addition. However, for a $100 block set, I think this sharpener is an excellent addition.
If you have quality sharpening stones and great sharpening skills, your money is spent better elsewhere. If you're willing to accept "pretty good" results for $29, then this might be a great product for you.
If the price point were $100, all of the ratings would have dropped considerably. Price was most definitely a factor both in choosing this sharpener and in how it was graded.