I fished 4# Vanish all Fall. Didn't have a problem. Seemed to be durable and good castability.

got to agree with Trout About, use it when it's cold and you'll find out why it's called vanish.

I used Vanish one time, it was 20 degrees outside, water temp 34.  Line memory was terrible and had several breakoffs.  I have given up on fluoro for the main line.  I use Trilene Xt 6 lb on the main line (or Siglon F in extreme cold), then frog's hair (flouro) as a leader.
 
IMO, The brand line is not as big of a concern, as making sure you re-tie often, spool the reel correctly, and change leader periodically.  Keep an eye for line nicks, etc.

Regardless of WHAT brand flouro you use, sometimes using flouro instead of mono can make all the difference.  A couple times I have fished 4 lb mono, same technique's, places, lures as someone else with flouro, and I didn't catcha  thing.  Literally the first cast after I tied on some flouro, bang, starting cathin em!  There's something about it that really makes a difference. 

I am trying Stren Magnathin this year, I used it on a trip to erie on new years eve, it really aint that bad for the price, I usually use tectan for trout fishing in streams by my house, but it has been known to weaken real fast, but when its fresh its the best line I have ever used, I use 3.3 lb , works amazing when the waters get warm and the fish are selective and have learned their lesson about being caught a time or 2. anyone else using this new magnathin?

all have ideas that work for them personally i use strait 4 lb test gamma clear co polymer all the way to jig no leader etc less down time means more time in water and more drifts per day.

I don't fish steelies, but I might come up on the first big run next fall and get as far upstream at ("insert a popular spot I shouldn't mention here") and  then start letting bare line run downstream till my spool is empty to straiten it out..... 

vanish transition is horrible in a lot of ways. to me its stiff,has very poor knot strength and a royal pain to use on spinning gear. i tried using it for a longest time and i just couldnt take it anymore so i switched. i bought a couple spools of p line halo.....just as bad as the transition but for different reasons. the p line degraded so fast (within a week) that everything broke off. 7" bass were snapping 6 lb line. i went back to using mono after that...i spooled everything up with suffix elite or power pro and said the hell with it. until....
 
i went to georgia and swung by bass pro shops in atlanta... i took the plunge and bought 2 spools of the new berkley flouro in the gold boxs. WOW is all i have to say. it smokes all the flouro ive used on my rods and on other people rods by a long shot. i put 6lb on my drop shot rod and 8 lb on my shakey-head rod which are both spinning rigs. i just got back from atlanta yesterday and after 6 weekends of using it this is what i found.
 
1. almost as sensitive as braid. braid still rules supreme but this stuff is pretty dam close
2. not as much line stretch as the 2 other flouros i used for the long term
3. doesnt degrade anywhere near like the halo
4. knot strength is leaps and bounds better then transition
5. as managable as mono on spinning gear, not like most flouros that loop up.
6. not one line twist yet. (good reels play a big part in that though)
7. good abrasion resistance. i had frays from pulling the shakeyhead through stump fields and managed to get all the fish i hooked in.
 
only downfall is it isnt cheap but most flouros arent and if your a line watcher no transition to help you see it. starting monday i'll be ripping all the line off the reels that currently have mono or flouro and replacing it with this stuff. i wouldnt touch any other berkley line with a 10 foot pole but this stuff is the total opposite. if you hate the line your using right now i would seriously suggest you give it a shot.