1 - the speed of order fulfillment. I ordered Corsa windows, they called back 6 days later and said they were ready to install.
2 - the quality of the windows is high in comparison with other manufacturers.
3 - a pleasant female team.
4 - a small minus: one broken window sill arrived (most likely during transportation), but they quickly fixed everything and gave a new window sill without defects. I ordered 3 windows, installed 2 of them myself, there were no problems with them.