i had the first ones in the uk a while ago.
pluses:
very VERY light
accurate, almost but not quite on par with a boomstick id say
very quiet...probably the quietest barrel ive shot, not sure if its due to the material or not.
looks bling
downers:
short control bore....if you were using undersized paint the accuracy may be an issue.
ive seen some nasty photos of what happens when they take a bad fall......just shattered mess!
fibres can eventually fray from dings.
i got mine for the half block cocker i built, i was on a mission to make the lightest marker possible and it definatly helped! however id say that on most guns you will find that the marker becomes back heavy these barrels are that light wieght