Lol, what a bunch of haters. Have we all been so enamored by the Anova that we can't see an awesome idea when it arrives?
Here are my thoughts, as a sous-vide-at-home addict of 4-5 years:
Price: Always the biggest factor when getting people to buy something completely foreign to them. What I like about this is that you don't have the usual caveat of "You'll also need to buy a vacuum sealer." More on that next, but whatever people pay needs to get them everything they need to cook sous vide.
Ease: No vacuum bags is great. Not having to learn the displacement trick for ziplocs is even better. I'd be interested is seeing exactly how open bags are used in Mellow. It needs to be fool-proof; one spilled bag of food and a new sous vide-r will be turned off the method.
Size: Too small - Not enough room for large roasts, lamb legs, etc. Too big - No place to put it. The integrated bath takes up a lot of room when not in use. I like that you're taking an aesthetic approach, that should help. Maybe advertising that Mellow doesn't need to be on the counter could help. Kinda in the same way people (who are lucky enough to have them) keep their centrifuges in the basement, rather than the kitchen. This and price will probably be the biggest challenges.
I love the cold to hot idea. I've played around with filling the water bath with ice and water and plugging the unit into a timer (the type people use to turn the lamps on and off when on vacation), since the biggest downside to sous vide is long cooking times. I think you may have the best solution to this problem so far, but the interface will have to be very intuitive.
Of course there are real concerns about food safety (as everyone here has jumped at), but your concept won't have that problem. If of course the 10 minutes from cold to cooking temp claim needs changing, the dynamic can change, however, I've noticed many home cooks here exhibit restaurant-level concern about food safety. Fine if you have food sensitivities, but overkill (in my opinion) for the average home considerations.
That said, I have a hard time with the 10 minute claim. It seems a bit optimistic. Of course, my (home built) bath uses a 1500 watt heater on 5-8 gallon bath (depending how full it is). The bath is extremely well insulated, and it still takes 30+ minutes to go from ~10C to 70C. I also cant remember how big the bath on Mellow is, so maybe my math converts to the 10 minute claim.
Controlling it from a smart phone... YES! Even if there was no cold-to-hot capability on Mellow, the ability to turn the bath on from work and have it ready to drop food in when I got home would be great. Its the more elegant solution to filling the bath with ice and using an old outlet timer. Do me a favor though, don't ruin this with a subscription service. Connecting directly to devices on a home network is far from straight forward. Many companies end up using a centralized server the user sends commands to and to which the device connects in order to receive the commands. Of course there are costs with this, but charging customers a monthly fee is a huge turn-off.
I'm stoked. Please keep us up to date on your progress in this thread. There are lots of sous vide pros here who can give great feedback, but more importantly, many have spouses who can serve as test subjects for the new-to-sous-vide crowd.