I have been monitoring and participating on this site for about 6 years. The brand name Crestline strikes a special place in my heart as I used to live only a few minutes away from their main manufacturing facility, and have used their products for many years. I cannot recall having a specific problem with their products nor can I recall a string of posts being negative about them.
I imagine they are like any other good manufacturer like Pella or Anderson, I you use their bottom of the line "spec" window the quality will not be as good as their higher line window.
Dodgeman