Tried the flat backstrap at the range and had the same experience as Klebrun - more secure grip and better accuracy. I find that with the curved backstrap the gun points a little high. With the flat backstrap the height alignment is better and the gun seems more secure when fiiring. When I bought the gun it had the curved backstrap on and felt great in the store and dry firing at home. However, on the range the flat backstrap seems to work better. I guess you never know until you actually shoot the gun.
I'm very happy with this purchase. After three range sessions my accuracy with the FNP-40 is approaching the M&P 9mm that was my favorite pistol until I bought the FNP. DA trigger pull is smooth and not too long. SA trigger pull is great. It points naturally and is softer shooting and more accurate than my Glock 23. Flawless through 400 rounds, 300 of which was JHP. The Glock will be gathering dust.