I have one of the new 580 series minis and like it quite a bit. A year ago I sold my old mini ranch in hopes of finding a little more accurate semi-auto better to my liking. I cannot get used to the ergonomics of an AR-15 (been shooting traditional stocks for over 45 years), even after a long-ago stint with them in the army. A close friend just bought the Keltec SU-16 and I find it way to light and his is prone to jamming with several ammo types and magazine brands. Well, after a year of fruitless looking around and trying other stuff, I ended up with one of the new minis.
I like it much better than my old one. Even though I scoped mine, I have noted the iron sights are MUCH better than the old flip-up ones. I sighted them in before I put my scope on and found them easy to use, easy to adjust, and rugged.
My new mini is more accurate than my old one, holding five shot groups of about 2 1/2 inches at 100 yards with cheap Winchester White Box 45 grain hollow points. I have not tried any other ammo yet. Neither of my minis has ever malfunctioned with any type of magazine I have tried. Right now, with the new mini, I have the factory 5 rounder, a John Mason ten rounder, and two factory 20 rounders.
I would not want this for my only varmint rifle - no way. When I am doing long range varminting or target shooting, I take my Sako 75 .223. But for a generaly beater/farm/truck gun, the mini is working just great for me. My old one took a number of chance encounter coyotes, and I am sure the new one will also.