As others have said, it can damage tips but I think its a fairly easy problem to get avoid. I dont use the guide at all and stop while the tip is in about the middle of the belt. After I started doing this, I havent had any problems with rounded tips. If you dont drag the tip off the belt, use the proper grits, and practice on a couple of cheap knives first, the wskts is safe for any blade. Like all powered sharpeners, it can mess up a blade fast if you dont use it properly but that's just the nature of the beast - if it can sharpen a blade fast, it can screw it up just as fast.
As I said, I dont use the guide so I hold the knife straight up to set the angle. I use the device at about waist height so Im almost directly over it when sharpening. Straight up and down is 20 degrees a side if the wskts is on a flat surface. To use different angles I set it on an angled surface which is just a small board with whatever's handy propping up one side. I set whatever angle I want using an angle level. i.e. 5 degrees will give 15 degrees a side when subtracted from the default wskts 20. When using this method, I can only use one side of the triangle (other side would be 20+5 instead of 20-5) so I use my left and right hands and go in opposite directions.
All in all, I have to say that I can get better, more consistent results with the wskts than anything else. I can do ok freehand (arm hair shaving, phone book paper push cutting) but my bevels arent near as nice to look at as some of the experts here. With the work sharp, I get the knife just as sharp or sharper in a fraction of the time, and the bevels look a lot nicer than my freehand sharpened knives. Im still trying to get better at free handing since I like doing it, but I doubt I'll ever be able to match the results I get with the wskts no matter how much I practice. If I was only interested in function and not the hobby aspects of sharpening, I probably wouldnt bother with free handing at all since the light at the end of the tunnel is so far off (the light being the ability to get knives sharper).
tl;dr - the wskts is a great tool. Its fast, gets knives very sharp with a minimum of skill, and wont damage your knives if used correctly (note - in my case, correctly isnt according to the manufacturers instructions).