Just a noob suggestion, I printed the tightner rotated Z 180deg with no supports. Reason for this is my first print I printed both together but the tightner broke at the screw hole while taking it off the heat bed.
Nice work. I love the concept of tensioner and clamp at the same time. I don't mind the left side being a bit tight. we don't want that to slip.
I took a spring from an oldish pen and placed that on the screw between the tensioner and the body. This just provides opposite tension for loosening.
By any chance is there one for the Y belt like this?