I should ask, "which one?" I've had three, now have two.
I started out a couple of years ago, bought a used 9mm version, and had quite a few issues with failures to feed and some not-quite-into-battery problems, which I first attributed to my handloads, but I had the same issues with a box of factory ammo.. I sent the pistol back to SA, they had it for a month, and it ran perfectly when I got it back. The repair sheet said they pinned the ejector, replaced and tuned the extractor, reamed the chamber and polished the feed ramp. SA didn't charge me a dime, shipping was free both ways, and I'd told them up front I had bought the gun used.
I had been looking for a .40S&W version, which SA had pulled the existing inventory and then stopped making them. I finally found one, but the guy selling it said it had to be a package deal with another 9mm. he had one of each, with hard cases, Kydex holster and double magazine holders, plus a soft IWB holster for each. So, I bought them both, and when I fired them they both ran fine. I kept the "new" 9mm and sold the one I'd had worked on (actually traded it and some cash on a M41 S&W). I've only fired the "new" 9mm a few magazine loads, I don't shoot 9mm much.
The .40 version, I started having similar issues to my first 9mm, but when I started troubleshooting and looked harder at my fired cases, I saw some pressure signs; a few pierced primers and several more flattened ones. That surprised me, because I was having no issues with the same ammo in my .40 BHP. The ammo was running just under 1250 fps MV with a 155 grain JHP. So, I made a batch and dropped it one grain (using Longshot), which dropped the MV down to 1100 fps, and it's run fine since then. I was about ready to send the .40 EMP4 back to SA, but I'm holding off to see what a couple hundred of the lower-power loads do as for reliable feed and function.
I hope this wasn't TMI for a simple question. I really like the feel of the EMP4, and when it's running right is as accurate as I can shoot any of my other guns.