The only relevant non-TK use of TK miles is for partners that don't have fuel surcharges. (not a long list) Sometimes you can book online. More often a lot of work is required - highly motivated and experienced members only...

Spending TK miles to upgrade TK flights costs the same as booking an award ticket in Business Class, so you only really want to do that in certain specific situations.

Most of the time, I just spend TK miles to book Business Class award flights on TK. The surcharges are reasonable enough such that the convenience and generally exellent TK hard/soft product make this work for me.