In summary: Unprofessional, uncaring, unplanned, extremely late.
Constella bygg was in charge of building 4 etage apartments in our bostadforeningen in Södermalm. One of them was mine. They won as their price was lower than the competition.
During the whole project attention to detail was almost nonexistent, and they would most often chose the cheapest option, and try to do as little as possible. Lots of mistakes on the way - with need to re-do things several times. At least 2 of the people in the apartments they were following ´burned out´ (brinna ut) due to the stress that their delays, lack of communication, and need for micro-management caused. When I confronted the person about the burn outs, his answer was that it was normal and it ´happens all the time´. During the project nearly everyone that was trying to reach them either got no answer, or got answers weeks late. As we were living in one of the apartments where they were working we asked if they could please let us know if advance when they would come. The answer was that they could not know, even a couple of hours in advance, if they would come. It was ´impossible to plan´ apparently. So they would just enter, without even knocking, at any time of the day (and sometimes night). This lasted for months, several days they would not show up, then come a random day, and so on. Once, one worker entered in the apartment at 1am while we were sleeping. I have no idea if it was for work, or to get a few hours sleep thinking we were not there.
They were months late to finish the work they were assigned, with a lot of tings to fix left over. Now the project is over one year old, and as I write the heating they fixed is not working in any of the apartments. We have contacted them weeks ago for fixing it, with no answer, so most probably we will have to get another company to fix it.
They may be ok for small projects, but avoid this company for any large work. Go for the more expensive options. It will be worth every sek.