I am somewhat of a craftsman and have been addressing knife sharpening with stones (manually) for many years. This was an arduous task as honing is an art that requires time, patience, and most importantly, precision to maintain a 20 degree angle. To be frank, I elected to give up knife sharpening by hand. I did my homework and read many product reviews before purchasing the Chef's Choice model 1520. It was expensive but, no more so than buying multiple stones of varying grit plus my time.
Upon sharpener arrival, I immediately went to work on our knife sets. Was I impressed with this tool - yes!! It was fast. The sharpener took only 20 minutes to do my entire drawer. It was precise as it held both the 20 degree (German knives) and 15 degree (Soduku knives) angles by virtue of the tool's design. The finishing hone provided the edge which the diamond faced stone had prepared. I warned my wife that the paring knife was sharper than new but, she cut herself anyway.
I also had a Gerber 7" knife which was 10+ years old. Gerber is out of business now but, they were renowned for manufacturing knives which had the ability to retain an edge. That is, their knives were made from very, very hard steel. However, all knife edges succumb to time/use and my knife died years ago. I could not sharpen the Gerber knife with my stones so it mostly sat in the drawer. The Chef's Choice made short work of the Gerber's dull edge by returning it back to the sharpeness I remembered and wanted.
I then did my neighbors knives and, on the following weekend, my daughter's household knives. Very fast, very sharp. I justified the sharpener as an heirloom for the daughter. In the meantime, I will keep the neighborhhod sharp.