What is it you are looking for feature wise ? Is it the fat foam grip ? If so, Harken, Holt, and Ronstan all offer aluminum extensions that have it..
As mentioned above, you can also come up with your own grip.
If you are just starting out in the Laser, I'd say the fact that the aluminum extension bends (only when sat on, or held on when falling overboard) can be a plus. Some of the carbon extensions will just break in the same conditions.