I have only just got my sharpener and I haven't really had much time to do much yet, but I thought I might give a few impressions that I have so far.
I'm not a fan of the guides - I tried one knife with the guide and I didn't like it. I can't see what's going on with the guide in place and there is too little control. Maybe I'd use a guide for sharpening scissors, but for knives I just don't like 'em.
Using the tool freehand: so far I can see this being really good - I can see the edge and the angle is easy to approximate. For convex sharpening I don't think that the exact angle hold anything like the same importance as it does for a V-grind - you are going to be hitting the edge no matter what. It is easy to hold the knife with a shallow, normal or wide angle to the belt and near enough is likely to be good enough.
I put a useful edge on a couple of kitchen knives and used the paring knife to slice a tomato and some cucumber - I was able to slice much thinner than previously, I didn't get the edge to 'hair whittling sharp' or anything but it was definitely a useful edge for the kitchen. I took a large kitchen knife and sharpened it - completely balls it up and had it sharp only half way along the edge, the other half was as blunt as a butter knife. I tried again and in less than half a minute the entire edge was sharp - wow, this sucker can work fast (220 grit belt). For these knives I am happy if they can slice tomatoes and cut potatoes and other vegetable and also cut meat - if they can handle normal kitchen task much easier than before I sharpened them then I am happy with the result. So now I am happy.
One negative is the belts - 80, 220 & 6000 grit is a bit limited. I'd have liked to see maybe 80, 220, 800, 2400 & 6000 as a basic belt selection. The 6000 is good for polishing and I am thinking that I DON'T need a leather belt or anything like that - the 6000 grit belt can be my polisher. The 80 grit is plenty course enough - I'm sure it can cut quick enough to put a new edge on that axe or machete quick enough. The 220 seems pretty good for convexing and edge & getting it sharp, but it can take a bit too much steel off fairly quickly so if you aren't careful you could butcher a knife before you know it - an 800 grit belt might be better for finer sharpening without grinding off the steel nearly so fast. A 2400 grit belt could give a polish/sharpen to a knife that doesn't need much, whereas the 6000 grit belt is pretty much just a polish.
Overall in general use this sharpener impresses me - I don't have a workshop with a handy spot to set up a 1 x 30 belt sander, but the Work Sharp Knife Sharpener can be used on my lap sitting at my computer desk. It can be used damn near anywhere, it really is small & light enough to be truly portable and use in any part of the house where there is enough room to sit down. When using it without the guide it is easy to see that the belt is flexing so that the edge is getting convex sharpened - for convexing on a small power tool this is the way to go IMO.
For the Aussies that are keen:
http://www.jaycar.com.au/productView.asp?ID=MF1082&keywords=250w&form=KEYWORD
For fellow kiwis:
http://www.jaycar.co.nz/productView.asp?ID=MF1082&keywords=250w&form=KEYWORD
This power converter seems to be able to handle the requirements very easily and isn't much dearer than the 120W version. It claims it can output 2.1A and the tool only needs 0.7A so it shouldn't get very hot and it should last a long time.