Everyone's got their favourites...and pet hates! F1 falls into the latter for me. I tried it in 15lb & 35lb in the titanium. I first put the 15lb on my 7HT mags when they first came out & went for a little session on Blyth beach. First cast, seemed to cast nicely, sat in the tide ok with a nice bend in the rod tip. After about five minutes tip sprang back in a classic slack-liner....however, I reeled in to find not a fish, but my rig, leader & about 50yds of mainline gone. Chucked out with the other reel & exactly the same thing happened again, so I packed in & went home.
When I tried the 35lb stuff up at Newbiggin one day, it took only the slightest brush up against a rock for the line to snap at that point when pulling from a snag. With a second reel on, I found that when snagged again, this time with no weak point in the line, that I had to walk back for miles pulling for a break - it was stretchy as hell!
So I binned the lot. Friends I know who do use the stuff, and seem to like it, are all using the black stuff - so maybe there's something to be said for using the different colour....but personally I wouldn't even use the stuff for rotten-bottoms
Only stuff I liked from Ultima was their Powerflex shock-leader.
Stuff i used was the Black one. Mainly for its thin diameter. Soon binned it, couldnt stand the stuff. It always looked & felt to have a twist in the line.