I thought it would be that simple, like just put a piece of plastic in there and be done with it. But when I started looking I found it to be a little more involved. What worries me is the intonation. The guitar as is is pretty accurate but there is too much buzz up high that I attribute to the damaged saddle. I read the specs on it and it is made of tusq and I even stress over that. Like does that mean tusk as in walrus tusk or it that short for something else? I'm starting to sweat right now/I used one from guitar center that their tech had and just pick one. My guitar isn't as nice as a Martin, 30 year old Fender acoustic, but the prefabricated saddle worked and put the strings at a good spot. I think they are made to a depth standard, but you might have to get it "customized" for your setup. I am not as picky, as I am not a guitar player, I just play guitar.
It is a simple job for a guitar tech and wouldn't cost a bunch anyway but you can do it yourself. First, do you have under-saddle pickup on there because that may influence your decision? Under-saddlle pickups demand that they have even pressure along the entire length to sound balanced. If you don't have undersaddle then you can simply find a saddle the same size or near to and sand/ file to fit the slot and action. A lot of Martins have compensated saddles where the saddle is graduated to accommodate for intonation where possible. That only applies to single type and gauge of string..
When I fit a new saddle I also carry out an inspection of the bridge plate and pin holes as well. If the saddle has worn badly the chances are they have too and will need attention. That can be more expensive.