Update: Since writing this I have replaced the flex-coupler with a u-joint and the combination of the BZB and the u-joint has is providing an even better result

This upgrade is intended for a stock Tevo Tarantula with a z- rod that is found to wobble and where the user notices z-banding.

First checks.

The Kit Tarantula implements a stepper motor at the top with a z-rod hanging from a flexible coupler. Before you go through the effort of printing and installing this upgrade, do the following verifications

1. Ensure that the acrylic bracket on which the z-stepper motor mounts is exactly square to the frame. (as seen from the side) Use a small square to measure this. If it is not square ensure that the horizontal extrusion is flush against the vertical extrusions on both sides. If it is flush but still not square, use a shim on one side of mounting screws along the length of the bracket to shim it until it is square. Fasten the t-nuts. Verify again.
2. Measure the distance of your z-rod from the vertical post. It should be the same at the top and at the bottom. This should be verified from the side view as well as from the back view. Adjust the motor position on the bracket and the lead nut mount on the X-frame until this is true.
3. Move the z position in big steps by using the stepper motor. Position yourself so that you can see the flex couple turning. If the flex couple wobbles then do the following. Tie the X axis extrusion assembly to the top bar with a piece of thin rope. Undo the flex coupling grub screws. Screw the z lead screw manually downwards to remove it from the coupler. Remount the flex coupling to the stepper motor axle. The axle must go only as deep as the non flexible part of the coupler. Tighten at least one of the grub screws. Now align the lead screw with the coupler and screw it by hand to it is inserted into the coupler. The lead screw must go only as deep as the non flexible part of the coupler. Lock all the grub screws on the coupler. Check that coupler wobble has been resolved. Repeat step 2 above.

Remove the rope

Position the lead nut about halfway up the travel range (i.e. approx 100mm above the bed) Move the z-distance of the printing head by using the stepper motor while watching the bottom of the lead screw. If the lead screw centre line is projecting a small circle (wobble), read further. If not then you should be good.
If you had to make notable changes in any of steps steps 1 to 3 above, do a test print. If you still have notable z-banding and you have notable wobbling of the lead screw, then you may try this upgrade. Note that this mod will not work if you support the bottom end of the z-rod with a bearing. In that case you will be better off with an oldham.

Extra Materials required 4 M4 x 12mm socket head screws 4 M4 washers (another four is optional) 3.9 mm drill bit (for those living in the imperial countries a 5/32" bit will do the trick) 3 mm drill bit (1/8" is good here) Synthetic grease