the only real cons I can think of since you like how both feel and both have good reputations for reliability are.
XD has lower ammo capacity
M&P has a horrible trigger
pick your poison. I'm a XD man all the way, never have been able to get past that trigger on the M&P enough to recommend them.
Not everybody knows about FN Firearms, let alone ones not in video games.
And the FNS is a new gun, maybe he hasn't heard of it yet.
Hmm...maybe he would check it out and like it! Oh no! That would be a shame
FN Herstal is a big name in handguns, if you haven't heard of them then you haven't tried researching very hard. the FNS has been out for over a year already, I would hardly call that a new model. also I have played with the FNS quite a bit. in my experience:
1. it is more expensive than the XDM, making it one of the most expensive striker fired, polymer framed guns out there that doesn't have HK stamped on the side.
2. trigger has the same goofy hinge in the middle concept that is on the M&P that likes to feel like you are squeezing a cheese stick rather than a trigger.
3. the fit and finish is the absolute worst I have ever seen in a gun that costs over $650, a $300 Ruger P95 has nicer metal finish and sturdier polymers than any of the FNS that I have handled. considering that both of the guns discussed here hover around $400-450 and both have better fit, finish and use plastics that don't feel like they belong on a NERF gun I would heavily recommend them over the FNS.