I use it and like it. I haven't used Astroflight myself, but I have seen the test results that showed 8190 to be superior in lack of stretch/creep and durability. I imagine AF is still a good material, but 8190 is better.
Endless vs. Flemish is a Ford vs. Chevy kind of question--depends on who you ask. I use both on different bows. Each has a slight advantage over the other in different ways.
I don't know of a string making forum, but I'll be happy to discuss them with you over the phone, via e-mail, or here.
Chad