Stayed at the apartment by the Chocolate Museum (approximately 1.5 km from the Dom), and began by walking there with my wife and our 2 young children (ages 4 years and 7 months), only to find no sign and no reception. The staff failed to notify us that we needed to pick up the keys at another address (near central station), and this information was buried in fine print on page 4 of our booking confirmation from booking.com. The NH hotel next door was kind enough to call the Domappartement to clarify the situation for us and then also call us cab so that we could get the keys.
Upon arrival at the Domappartement office, I said I was there to pick up the keys. The owner asked me how I liked my trip so far and I told him that it sucked because I had walked 20+ minutes with two young children and several bags of luggage, and that I had to have a cab drive a us there and then back to our room, and that the cab was waiting outside. The owner first said "Not my problem". Then he told me if I wasn't more patient, he wouldn't give me the keys to the room at all. I have never been treated so rudely at a hotel EVER--and I have stayed in youth hostels as well as 5-star resorts in more than 30 countries and 5 continents.
After this, we arrived (this time via cab) at the apartment. Though it claims to be a 4-star establishment, this place was nothing short of an unclean family room at a youth hostel. Though the owners said they had "made up" a bed for our 4-year-old, but this effectively meant they had put some torn sheets and a blanket with dark hairs on the sofa bed. Which is to say that the sheets were sitting on the side of the sofa, not that the bed had actually been prepared to sleep in.
As for the place itself, the bathroom was totally substandard and came with no soap or shampoo and only 1.5 rolls of toilet paper. The kitchen constantly ran out of hot water and was poorly appointed overall. The floor was unclean (not good for having an infant just learning to crawl) and the bed was incredibly uncomfortable and the pillows were flat and some didn't even come with covers, as did a number of extra blankets that felt as though they hadn't been laundered in ages.
In spite of these enormous flaws in management and property (which in our case was at least 20 minutes from the center), I was willing to leave the Domappartement a fine review. Until I went to check out. There, the owners tacked on approximately an extra 90 euros, claiming that having a child in the room required more cleaning. We left the place spotless, and no one ever came to clean it once during our stay. What is more, I had specifically called the Domappartement before our stay to make sure that we wouldn't be charged extra for having two children stay with us. The owner denied having spoken with me, and even though she couldn't provide a copy of the email she claims to have sent me, forced me to pay an extra 90 euros.
In short, the owners are rude and dishonest, and the apartments (or at least ours) are not nice and not in a good location. It felt like I was staying at some abandoned apartment with cheap, classless IKEA furniture with a view only of the ring road and the NH hotels dumpsters. In the end, for what we paid (over 100 euros/per night) we could have been in the center, with a view of the Christmas markets, and with a reception to pick up my keys and not have some arrogant owners attempt to deny me lodging because they failed to do their job.
In short, AVOID, AVOID, AVOID, at all costs. You will be glad you stayed elsewhere.