I did a DIY using the Stir Starter circuit diagram. I’m a fan of his use of the variable voltage regulator; it makes a lot of sense. I’m not a fan of his pics where everything is just soldered together in a blob instead of some sort of board; and I would like to see a power switch and a light. (added both to mine) I suspect with the pre-built you turn it on or off by plugging/unplugging; which I guess is fine. The other posters say they’re happy with theirs. Mine is very quiet in operation, which is something you might not expect with a fan-based design.
If you want to trick-out the thing with a DIY mod after you buy it. I glued a simple ferrite magnet inside the box near the corner, but away from the fan. I have a leftover rare-earth that I leave attached on the outside of the box. (Where the ferrite I glued inside holds it there.) When I’m done stirring, the leftover rare earth can get plucked-off the box and stuck to the side of my flask where it and the stirbar hold each other in place so I can decant without losing the stirbar. I suppose gluing some metal to the box would work to hold the stirbar retrieving magnet as well; and it could be on the outside, I just had the magnet I used lying around.