So i built one and it works. Only cost was the stir bar.
Lucked out with the box i chose (thickness of lid/space between magnet and the lid) and the strength of the hard drive magnet, because it spins in liquid without a speed control (or an on/off switch).
Here is my question:
How do I use it?
I boiled about 1ltr of water, added 3/4 cup DME, boiled another ten to fifteen mins, left it covered, let it cool
When it was cool, i opened my yeast--white labs 007, shook it until mixed, and dumped it into the glass vessel on the stir plate. Fired it up and got a nice cyclone in the middle. Left it running for about 5 hours.
Still no signs of life. Didnt have another vial so i got nervous and pitched it on my freshly brewed and aerrated wort.
Im reasonably confident it will kick off by morning but im also sure my "starter" did much more than increase my chances of an infection.
...sigh...maybe i shouldnt have experimented until i was more sure of the process...just got excited about using the new DIY homebrew gadget..