I received the darn thing yesterday and used it for my regular weekly tests today. Can't be happier - in under 30 seconds of mixing in completely dissolved the Hanna nitrate reagent into a clear solution - I was never able to completely dissolve it when I was doing it manually, without small bits still flying around.
The device is larger than Hanna vials, though, it rather fits Red Sea vials (made the titration test for calcium a breeze - I kept dropping the reagent into the swirl, until there was a color change - no need to shake after every drop anymore). For easily centering Hanna vials, I cut a thin slice from a 1/2" PVC tube and placed it there - the size is just about right, see the photos.
The only thing that makes me concerned about this little device is the magnetic bead. It is about the size of a rice grain and when it falls down, it is pretty hard to find. I'll order several more similar beads of different sizes, to keep a stock. Also, it would be nice to have a small potentiometer on the side of the device, to be able to change the RPM. The speed is a tad too high to my taste, and generates a small whirlpool in the vial, which tends to suck air from the surface. I think there is a small motor inside, with magnets attached to the shaft (as it makes small noise when I turn it ON even without the bead). It may be easy enough to add a regulator - I'll take it apart to look when I have time. But all in all, its $20 spent very well. Its rechargeable, BTW, charged in about two hours. Should be enough juice to keep it going for quite some time - I don't think the small motor takes much power.