I've noticed that with Matrix/Slitherine you are better off purchasing directly from them and getting the Steam Key later. Some of their Steam purchased products have issues with them regarding mods, updates, PBEM features, etc.
One of my recent purchases from last year was Field of Glory Empires from Steam. I had a difficult time getting the multiplayer window to log me in and find a game I was playing with Jason, MD, and Tuna. This is the 21st century and I shouldn't have struggles like this on a Steam purchased game. Forgive me but my patience and tolerance for ineptitude is quite short these days.