I'm a righty and this is one of two guns I use for IDPA, the other being a CZ75B. I shot the FNS 9 most of the year (2 matches a month) and the CZ75B the last four matches. I shoot the FNS 9 in SSP and the CZ75B in ESP, cocked and locked. Both guns are excellent for IDPA. The CZ might be a little more accurate for me (just a very little), but the trigger reset on the FN is shorter and I feel I shoot it a little quicker, so it's a toss up for me on which one is better. The FNS 9 would be perfect for a lefty, all ambi controls!
I use a Safariland 5197 holster. I originally tried a Blade Tech mag pouch but the FNS 9's mags have a tab on the side that dragged on the inside of the pouch and made it hard to get the mag from the pouch. What I use now is the mag pouch that came with my XD45. The tab doesn't drag on the side of the mag pouch and the tension can be adjusted to fit the 9mm mag.
I use both the FNS9 4" and FNS9 5" for USPSA production and 3Gun and love both of them. I run Sevigney sights on the 5". I use safariland holsters for both and use carbon arms +5 +6 base pads for 3Gun. I have close to 6000 rounds through the 4" with no troubles.