I bent my Streamlined extension. Don't know how, don't know when, I just tried to use it on a small extension the other day and it wouldn't fit into the mast. Couldn't work out why until I saw it looked like a banana. It is hard to see on a photo.
I still like the Streamlined for the same reasons as everyone else above, plus they come in 46cm length. The most I use is 34cm extension, but I like the idea of having the extra length in the mast. I do find the same thing with the pulley alignment and Severne sails as Gazman, though it is quite managable, but not as good.
So, I bought a new one. The new ones have a matt anodising, which I think looks better, not sure if it is more sand resistant though.
Also the new one has only a single rivet on one side holding the cup base onto the tube. The old one had a pin that went all the way through so held on both sides which would have to be stronger, although maybe perhaps not necessary ?
Would be different with a euro-pin I guess.