Our FTC team 3507 has used only Tetrix kits for 5 seasons now, but with the relaxed material rules of the last 2 years, we are phasing out use of very much of the Tetrix channel in favor of 20mm slotted framing with 10-32 assembly H/W.
As noted, the Tetrix axles are horribly weak and ill suited to high torque with bidirectional rotation. We will not use them for anything but low torque transfer purposes. The hollow 5/8" tube end fitting scheme, though improved with new parts is still not great either.
Tetrix channel is good for quick prototyping. There are also useful tricks, that allow overcoming some of its weaknesses. Some are shown in PICs below:
