T-corner to add ridigity and prevent X-axis wobble at higher print heights.
I didn't expect this to eliminate the X-axis wobble (I think you'd need to replace a large chunk of the frame to achieve that), but thought it would at least make the frame stiffer, which it does.
There's a definite and easily noticeable difference in the rigidity of the frame - you can tell just by pushing on it from the side before and after installing the T corners.
The T-corners installed very easily and firmly - they are a very nice fit for my frame. I had no issues at all with putting them on.
The only issue I had was that, despite the 8mm brim, one of them fell over at 98% completion and I aborted the print when it happened. At that stage there was no need to re-print since it was basically done, and they work just fine.
The pieces are quite wide at the top compared to the base, so I guess there's a bit of leverage happening there if the print base is not exactly adjusted and the print head is pressing slightly on one side, which is probably what caused the toppling. I notice a couple of others have had this problem as well when making this.
If I were to do it again I would increase the brim size a bit - maybe 10mm or even 15mm - just to be sure. These are fine as they are though, and I'm very happy with the result and the increased frame stiffness.