I haven't had any major problems. I used them quite a bit this past summer. The WFF lines (I have several in the 5wt-8wt categories) all float well. I've never had any problems with cracking or anything. (I usually keep my rods strung up and ready to go in the back of my Pacifica, and usually don't cover the reels. So, although the rear windows are all tinted, they still probably get pounded with UV rays for many weeks at a time.) They definitely cast well.
Are they the best lines out there? I really can't say (cuz I don't know). For what I paid for them, they are awesome!
I like the white color best, and the greenish color 2nd best.
I have some of the 8 wt sinking lines, but haven't actually tried them yet.
David Merical
St. Louis, MO