I did my last build with one. It was a double action single set trigger. The one they sold me was a Davis trigger. Pay close attention to the profile of the gun you want to build in the trigger plate area, because this TP is really thick there, meaning you won't be able to bend it. to get a bend in this area you will have to file it in. And even if you do (heat and bend it), the bend is going to throw off the set trigger engagement.
The forward throw in setting the trigger necessitated bending in a deeper bow in the trigger guard (to allow for the forward sweep in setting the trigger) than was typical for the original style. A small thing that you would have to be really looking for to see.
This thing is pretty tall so to get it down you will want to file down the blades as thin as possible
The internal assembly is 3 different blades hung on one hinge pin. With mine the holes were larger than the hinge pin, so it created a trigger with a lot of side to side play, or rattle. I HATe rattly triggers! To solve for that I went and bought a numbered wire bit and drilled out both the hinge pin hole AND the 3 blade holes. Then I broke off the drill bit and used the shank as my hinge pin.
In using it, it seems to work pretty well, and is a pretty cool feature, but it was a LOT of work that in the end I really don't think was worth all the effort. If I were to do another gun with a single set trigger, I would opt for a plain single set trigger rather than the double action one. Since almost all of my shooting is at paper of other inanimate targets, I rarely shoot the gun in the non set position, so that feature is of limited worth (to me).