I had the 12” Carbon tube and it was eventually enhanced with better main mirror support. Optics are very good, I cannot tell any difference for my Planewave 17” CDK, perhaps due local seeing not so good. Of course Planewave has bigger corrected field and better mechanics, but If I could now choose. I would kept the GSO.
In my blog you can find out what I did to this GSO 12” CF tube model:
https://astro.galleria.fi/blog/