Finally got to try a Darwin at Philly Vapefest as several people had one. I will say that the photos of the unit do not do it justice. It is all metal and has some nice heft to it (probably only slightly lighter than a Provari) and by all appearances is a well-made device indeed. For 99% of would-be buyers, the lack of an easily removable battery would be a non-issue, just another device (like your cellphone) that you will have to remember to periodically charge either in a wall outlet or your car. Yes, you will want to have some sort of back-up device just in case but you will always want to have a back-up device for anything you rely on.
One small knock on the Darwin is if you have a drip shield on your atomizer, the gap between the swiveling arm and the body of the device is not enough to allow the atomizer to fold back in line with the device all the way, but that's a pretty small nitpick.