The dual z upgrade is actually used on an Ender 3 Max and it worked out very well. The z screw is longer than needed but it fits without a problem. I was very impressed with the service I got from Spool3D. They were willing to measure the screw and verified the length before making the purchase. These guys are top notch!

I used the Creality branded CR-10 dual Z upgrade kit on my Ender 3, and the procedure is almost identical as for the CR-10 except for the orientation of a couple of bolts. I had to increase the Z stepper Vref. The two stepper motors were too weak at first and would skip. The original Z Vref was 0.55 volts and I doubled this to a bit over 1 volt on my v4.2.x driver board. The new stepper motor and wiring also caused the LCD display to get scrambled and messed up due to electrical interference, including random button presses. I fixed this by isolating the display from the metal frame where it is screwed on, using the plastic spacer found here: https://www.thingiverse.com/thing:3077155 I also replaced the two M5x8 bolts with smaller self tapping screws and plastic drywall anchors for electrical isolation. This totally fixed the scrambled LCD display. You could also use M5x8 nylon bolts. Update: I realized that part or all of the electrical interference problem may be due to the grounded metal case of the power supply having to be removed from the frame in order to position the second stepper motor and lead screw. So another solution is to ground your printer's frame to the case of the power supply using an extra wire. Update 2: If you want to print your own M5x8 plastic bolts for electrical isolation (instead of buying nylon ones), I tested this using PLA with a 0.12mm layer height and 100% infill. I have the required "M5x8.stl" file available for download here: https://drive.google.com/file/d/16I9_m7iFckemZd0B9ycZGz0n8H5BgKxX/view?usp=sharing

I used this kit to upgrade my ender 3 pro to dual z axis. I found this an easy upgrade. I cut down the Z screw to match the Z screw that came on the printer. The wiring was simple and straight forward. I am currently designing a power box printing that will attach to the side of the 40x40 extrusion so the power box will still sand up and not make the printer too wide.