This is the arrangement I use: the diamond gate. This setup literally prevents you from doing diagonals at all. You can only press the cardinal directions, and if you move along one of the edges of the gate you will most from one cardinal direction to the other without ever pressing both of them.

TGM in particular requires a lot of very precise switches between left/right inputs and up/down inputs, and you really don't want to accidentally inch into pressing down while you're trying to put a piece into place.

(Unfortunately I took this with the restrictor rotated a little so it might be a bit confusing, sorry. In the next post I put it on the stick and show it moving around so it'll be more clear there)

Here you can see the inner circle put into the middle and rotated to be used as a square gate. Once mounted like this, the corners where the stick can easily rest would be diagonal to the stick's buttons (which are on the four black boxes around the metal stick shaft).

This arrangement makes the stick work a lot like a dpad. You can hit all eight directions and easily shift between diagonals, but you aren't left with absolutely no guidance about where the directions are and when you'll shift between them.

This is probably the most common configuration for most uses. If the game you're playing wants you to use diagonals, this is very versatile.

But in Tetris you do not want diagonals, so, we're going to arrange this a bit differently when I put it in.

Pictured here is my restrictor plate taken apart, next to the innards of my new arcade stick. The larger plastic piece goes on the outside and the smaller circular piece is put into it and rotated to become either a square or diamond gate. I believe that if you just leave this inner piece out then you kind of have a circular gate, but I've never actually tried that.

Once assembled it'll go onto the clips at the bottom of the stick.