I bought of Croatian Spectrum for my own self build. I bought all PVC windows along with garage and house external doors.
If I was doing it all again I would run a million miles from these and go with someone else. The quality of the windows are of good quality but the service is terrible to say the least. In all my experience I have never come accross a more disorganised company which ultimately delayed my moving into the house by three months.
To give you an example, the windows came one month late (which in fairness I can live with in the grand scheme of things), however they didnt deliver my external doors, when I asked they said there was an issue on loading the front door, grand so when will I get the doors ? they said in 3 weeks. Ok 3 weeks isnt so bad but it turned out to be 2 months. When the doors did arrive there was an issue with the garage door being too big (it took two different doors before they fitted the correct garage door). My front door is bright orange even though I ordered a dark oak color !!! That turned out to be the least of my problems, the front door (which is made from timber) has warped and its only installed for the last 5 weeks !!!! So now the frame and door have to be replaced.
Theres more but I'll stop there. As said previous the quality of the windows are good and we are happy with them but the service leaves a lot to be desired. My only consolation is that I still owe them half the money, which if you happen to deal with them do not pay the full amount until you are certain everything is in order.