I have used several straight blade sharpeners over the years, and this I can describe as very capable of putting a decent edge of most knives. You'll not get a razor's edge as a result (razor = can shave with it), but it will certainly take off any burrs on the blade and with the fine ceramic side you'll get a nice even sheen on both edges of the blade. This sharpener weighs virtually nothing and can be kept in a pocket without knowing it's there.
If you after a serious sharpener, you might be better looking for a ceramic rod style sharpener from the likes of GATCO, which will allow you to put your own angle of edge on your knife, whereas with this Gerber you are restricted to their specific angle, which may not suit every blade.
All in all, this is a good sharpener, which is ideal for a camping trip away as a back up in case your blade gets dull - but probably not suitable for a permanent sharpener.