I can't for the life of me figure how they would work properly. Sharpening a knife with a slightly curved blade is tricky enough because in order to sharpen it, you need a particular angle (whatever the angle was at which the blade was originally manufactured). Every knife is different, and a professional sharpener will know or look up the angle for your particular brand & type of knife to recreate that angle when s/he is sharpening it.
So the first problem I see is that any one rotary sharpener would likely not be the correct angle for every brand of blades. The second issue is trying to maintain a consistent angle on a rotating circular blade so that it sharpens & does so evenly all the way around the blade. And finally, I kind of agree with Onebyone. Although, I think instead of sharpening the blade, it's actually honing the rotary blades. To get any benefit from honing, the blade must already be sharp. If you wait until it starts to dull, it's definitely too late (even if it's the proper angle for your brand of blades & somehow manages to make consistent contact with the blade all the way around)
Honing isn't a bad thing. It's what they do at the knife sharpener shop when you bring them a pizza cutter. It can prolong the life of the blade if done properly. Still, with an average price of $3.25-3.50 at Walmart & Amazon for genuine Olfa 45mm blades, I personally would rather not risk a dull, uneven or partially damaged blade so I just buy the replacement ones.