My feeling is most people get the Saiga for its shell capacity and quick reloads. Having a mag on it would cut down on time a lot.
My wife has a XDM 4.5 in 9mm. I like it, and it works well, but I talked to a gunsmith about aftermarket triggers for it, and he said it was not a drop in install and the labor was nearly as expensive as the actual trigger. In fact, he did his best to talk me out of it. On the glock, it's as easy as knocking out a few pins, tugging the old trigger out, and dropping in a new one - no gunsmith needed.
Look at Powder River Precision out of Oregon. They have drop in trigger kits for the XDM, and videos online to walk you through it, it is not that difficult.