I see your post is from February, so hopefully you have your extended mag. I bought the Nano in September and it came with the 6rnd mag and the extended 8rnd mag. I have large hands and don't care for the 5rnd, but the 8rnd fits great.
I've fired about 500 rounds through the Nano with no issues, using brass and steel cartridges, 115 and 124 grain. I also fired 16 of my self defense cartridges through the Nano as I've read some SDA hang up when loading into chamber.
No issues with my Nano at all... Love the smooth and compact design and the extended 8rnd magazine. I will be ordering a couple more of the extended magazines.
2 thumbs up from me on the Nano...