I wouldn't go for the FNP. There's a reason they sell the FNX in favor of the FNP: lower bore axis, better ergos, etc. Not to say the FNP is a bad gun, the FNX I'd just a better gun. I can vouch for the striker fired FNS being an excellent and supremely reliable handgun. It is more in line with the M&P comparison, and I like the grip on the FNS a lot more; better size and the texturing makes it nearly impossible to drop.
As for the concern of getting a recoil spring: I couldn't ever see it breaking because it's of a flattened helical construction (not a standard round wire spring), and I'm sure it's supremely reliable just like everything FN has ever made. If it were to ever break I guess you'd have to contact FN to get a new one. I'll cross that bridge (if) when I come to it.