CDNN buys up lots of guns from manufacturer's overruns, discontinued products and other sellers/distributors who are cutting inventory or going out of business. You can find some gems in their catalog, like the .45 long Colt snubbies by Taurus.
The FN Forty-Nine is kind of a "me too" polymer service pistol. It seems to have nothing special in the way of features. I seem to remember comments on TFL that its grip is kind of uncomfortable and the trigger pull is rough.
The Steyr M series is a more radical design. To me its best feature is a very low bore axis, which helps manage recoil. I've heard that the .40 feels like a 9mm and the 9mm feels like a .380. It has some other quirky stuff, like the "triangle/trapezoid" sights, the odd safety inside the trigger guard and the built in key lock.
If it were me, I'd take the Steyr before the FN, but only because I like odd stuff. You probably won't find either pistol as a range rental, so that won't help you choose. You could go to a gun show and see if you can spot them, at least see how they fit your hand.