Not an exciting topic, but pretty critical.. I have owned a
carbon streamlined extension system for a few months now...'extremely light' feather light I would say, just like their booms.
Again like the boom, they do it a little different in the way the pulley is set up , quite 'external' bit scary looking my toes thought!

but they haven't had any close encounters with the it, so all good there I guess.
The pulley has large wheels which make down hauling with some gusto a bit easier and the way the pulley is set up to the side you kind of just 'loop' your lines over the pulley rather than thread as such, cleating on/off is equally easy.
The base/deck like the boom head has a lot of 'alloy' rather than plastic, its a very low profile on the deck of the board and has a real snug fit... the Alloy thing means you may have to give it a bit more TLC than other gear.
I find the deck uni release button quite sticky, so I tend to leave my uni in to save the hassle, I chose the double bolt leave in board type, you could avoid this hassle if you prefer the screw on/off style, for me I like the 'safety' of the double bolt...memories of a 2 hr swim at Lancelin will do that to you!...Has a basic rope safety system for the tendon also.. haven't had to test that yet!
It also comes with really high quality Dyneema downhaul line...much better than the crap that is often supplied as standard fare with other brands.
There is also a 'hook' that slips into place around the 'release button' so you can't accidently press it in and release your rig, great idea and essential for this design, if it wasn't there I wouldn't use it as you could easily knock the button in.
Same as with the Streamlined boom, ultra light, ultra stiff, bit more fiddly but very high quality design and build, so much so that I managed to get the jam of all jams the other day , extension in the mast for ever, was never coming out, ever!..30+cam jammed into my ezzy mast ARRGGHH! Disaster!!! fine sand holding it all in place, this was seriously jammed!
What followed was a brutal rescue of the worse kind, it really should have broken bits..I actually BENT the first part of the metal pole on the gate and had to go to the base of the heavier pole! My rear wheels even spun a bit! I kid you not.. something should have broken..... not even a dent where the screwdriver was...
So I tried to bust the streamlined boom with a massive high speed reef stack..no go..just me broken...
And have tried to bust the carbon extension now also..no go...
There is something in this carbon stuff....pretty amazing really,
Think you will find on their website the spec's will show that the extensions are possibly the lightest, and I haven't felt a carbon boom as light as theirs, it amazingly light...but from what I can tell they don't have super big sizes in the booms, they are into the 'pre preg' carbon stuff and given all they do is extensions and more recently booms I think they are onto it.
Seems to be really high quality gear, and no more expensive than any other quality carbon product out there, would I save a few dollars to get an alloy unit instead of carbon..nope.. I'm sure it's going to last plenty of time, it's not going to anodise away, and yes it may only be a saving a 100 grams or so of weight, but I think if you can reduce your overall rig weight by a few hundred grams for each component , you are maybe a 1kg or so lighter overall, that has to make for a more enjoyable experience.
Biggest Plus - Lightness, Strength, Build Quality Downside - little bit fiddlier (at first) than others, perhaps more maintenance required than others, There you have it...Streamlined reviewed, Ask me again in 12 months, so far I would say a
big thumbs up, a great investment.