Just received my extension in good order. Installation was a breeze. I chose black, and it looks like an official TM part.
My desktop is fairly high (30in/76cm), but I was feeling optimistic and went with the 10" extension. It is still perfectly comfortable for me in both centered and offset positions. Any longer would definitely place the stick too high for desktop use, IMO. In-sim (DCS, Elite: Dangerous, Star Citizen) I have an uncanny level of control - the true utility of my stick has been unlocked.
I would highly recommend this product to anyone who owns a TMHWH.
Thank you, Sahaj! It was a pleasure doing business with you.