I've used the opamps and DAC in that device. I don't have the equipment to accurately measure specs such as input offset but they didn't seem that bad. Certainly accurate enough for 8-bit resolution. They are kind of odd in that you can't connect much to them internally - although as you pointed out they did include the DAC output in that - so I mostly just used them to replace an LM358 in some applications (low side current sensing, voltage follower, 2nd order filter for PWM etc..).
I'll admit I too don't really trust the internal opamps as they tend to be characterized rather than tested, but can come in handy. Wouldn't use for anything that requires accuracy.