There are advantages/disadvantages on both sides.
The Gatco clamp gives you "really" the indicated angles, it is larger and therefore less sensitive to blade width and thickness to "keep" these angles. On the other hand, it is asymetrically built, i.e. the angles on both sides of the blade are "very slighly" different, which should shouldn't bother at all (if you clamp the blade always the same way!). The hones are much broader and longer, giving you a nice speed advantage in sharpening, except for strongly recurved blades.
The Lansky clamp's angles are NOT as given,
unless your blade happens to have "ugly" dimensions. The clamp is very small, making it very sensitive to blade dimensions and clamping to duplicate a once set angle (well: you might resharpen, once in a while?).
On the other hand the clamp is symetrical. i.e. both sides of the blade will show exactly the same angle (IF you clamp it symetrically). The hones are quite small, which is a clear disadvantige, it takes more time to reach the same result. The ever loosening screws of the guide rods are a nuisance in my eyes.
Both systems do work, give perfect results (for small knives!) when handled correctly, but my (personal) nod goes to Gatco.
Do not use them on blades longer than 4" or so, you'd have to do it "in sessions".
Happy sharpening
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D.T. UTZINGER