Check it out as Hickok45 runs the new Sig MPX with a suppressor!
Get out your ATF forms, this is a great candidate to turn into a short-barreled rifle (SBR).
In the same vein as the HK MP5, the Sig MPX is a 9mm submachine gun. It has many similarities to an AR-15 but is not interchangeable. The standard arrangement holds 30 rounds, has an 8" barrel, and weighs 4.6 pounds.
There is much debate about pistol-caliber carbines as defense or service weapons. Regardless of your position, 9mm ammunition is cheap and nearly ubiquitous. Another positive to pistol calibers is that they generate much less recoil and blast than most common rifle calibers. They are also simpler to suppress.
The gas piston operating system is renowned for reliability; it is similar to an AK-47.
Warning: without ATF paperwork designating your gun as an SBR, you are not allowed to put a shoulder stock on this gun. (Apparently that law made sense to somebody, at some point in time...) You may, however, use a stabilizing brace such as the Blade.
As Hickok45 notes, the standard configuration feels like a man without a country; however, add a brace, a shoulder stock, and/or suppressor, and the Sig MPX shines.
With street prices a little over $1,000, you might have to consider adding one to the collection.