I've never been a fan of slow cookers because it pretty much just turns any meal into a flavorless mash of carbs and partially digested protein. Everything ends up overcooked. Perhaps because my slow cooker is junk with just a "low" and "hi" setting. the Auber PID controller sounds like a much better solution. It should be a piece of cake to replicate it with an Arduino, temp sensor and a high amp relay, after some experimentation and calibration with a candy thermometer, you could even "program" your meals.
Slow cookers are only good for braise cuts: beef chuck, chicken thighs, pork shoulder. You want to put some liquid in, but not too much. You want aromatics (a whole head of garlic, an onion). I never put starches in my slow cooker anymore.
The low-temp water bath is definitely much more precise. You can't cook a steak in a slow cooker; the cooker runs near the boiling point of water.
http://www.auberins.com/index.php?main_page=product_info&...
It would cost about the same to build it as an equivalently featured Auber device though you would have much more control.