With the recent tune up of my saw I invalidated all my ZCI's. Making these after you already have some is a snap. Trace out a few (don't forget some spares) and rough cut to size and shape.
You can pass on the double stick tape and just drive screws in where the adjuster screws were in an old ZCI. The hole the screw makes in the new blank will get eliminated when the adjuster hole is drilled.
A top/bottom bearing pattern bit is great for this because you can route part of the pattern, adjust the bit height, flip your material/pattern and always be routing downhill; no chatter or blowout.
I leave a little beaver tail at the back that I shape vs. using a pin but I've done both. My current batch will have a little bigger tail.
Getting the insert into the opening to make the initial cut is something I have seen some folks struggle with. Using a smaller blade or the outside of your dado set will work but, I just route a stopped groove. Since I already know exactly how much space I need based on the old ZCI its faster this way for me.
Put the insert in the throat, adjust for level, clamp it down (or lock your fence over it), raise the blade to make the initial cut, drill the holes for the MJ Splitter and I'm all set.
I do one for every blade I have and a couple extras for dados or angles. When you do them in a batch they don't take long at all.