The black double stack magazines are completely manufactured out of polymer, exception made for a metal elevator spring, and their catch is so sturdy that they require a generous tap to be inserted and won't fall free when released if completely empty and thus too light.

The pistol grip of the SDM SMG9 comes with thumb seats and non-slip serrations on both sides; a bottom plug can be removed, revealing a hollow stowaway compartment that will easily accept batteries, a small cleaning kit, or other similar useful accessories.
The sturdy polymer stock, also featuring a rubber butt-pad, is attached to the lower receiver through a metal plate. The stock is hinged on the plate, and a small and unobtrusive top button allows it to fold on the right side of the SMG9; said button must also be pushed to unfold the stock.

When folded, the stock is extremely close to the ejection window, but despite that, we found out that it wouldn't cause any kind of disturbance to the ejection pattern.

On the left side of the stock plate is the rear sling loop; the front loop is located on the left side of the front sight base.

Speaking of sights, the front sight of the SDM SMG9 is of the hooded kind, sports a round top opening and requires a tool to be adjusted in elevation.

The rear sight is of the peep type and can be adjusted in several positions, more akin to a modern AR-15 type sight than to the MP5 drum type rear sight featured in the early CS/LS5 sub-machine gun prototypes back in 2009.

The SDM SMG9 also sports a 11cm/4.33” long, milled top MIL-STD-1913 “Picatinny” on top of the upper receiver, allowing the use of optical or electro-optical gunsights. 

Three shorter Picatinny rails (3.5cm/1.3” of usable surface, 5,5cm/2.16” with their mounting base included) are located at 3,6 and 9-o'clock positions on the lower portion of the handguard, and kept in place by two flat Allen screws each.

Despite their small size, the handguard rails are more than sufficient to host any kind of tactical accessory that a shooter may want to install on his or her SDM SMG9; their major drawback comes in form of sharp edges that may hurt the shooter's hands in case of rough handling, plus the rail located on the left side of the handguard (9-o'clock position) is definitely too close to the cocking handle – meaning that most accessories would hinder operation if installed there.

My suggestion would be to use small-sized add-ons, or to use an Allen key to remove the rails you don't need.
Another component that sports a disturbingly sharp edge is the square cut at the top rear end of the cocking handle guide, meant to allow the shooter to lock the bolt in open position: watch out for it when operating your SMG9, or consider filing it away.

The SDM SMG9 is 46cm/18.11” long with its stock folded, and 69cm/27.1” long with the stock open. Its cold-hammer forged barrel is 216mm/8.5” long and sports six right-handed grooves, with a pitch that's more than apt to stabilize basically every commercial 9mm load out there; indeed, the CS/LS5 sub-machine gun the SMG9 is based on was conceived for very high-pressure loads.

The muzzle sports two step cuts, meant originally as attachment points for a proprietary silencer whose manufacturing status is not known at the moment.

We tested the SDM SMG9 at an outdoors shooting range in northern Sardinia in a sunny July afternoon.

Despite the manufacturing Company's claims about the CS/LS5 sub-machine gun being “ideal” to engage targets up to 80 metres in range (when using high-pressure 9x19mm DAP92-9 Chinese service rounds, mind!) we decided to replicate the average experience of a civilian shooter and test the SDM SMG9 on standard pistol targets located at 20 metres (21.8 yards).

We had our SDM SMG9 outfitted in an “Entry Weapon” configuration with a CAA Tactical MGRIP foregrip, a NexTorch TL1 tactical flashlight and a Vortex SPARC red dot sight.

The SDM SMG9 at the range

The polymer double-stack magazine of the SMG9 is available in a plethora of capacities, up to thirty rounds -- this particular one was limited to 15 rounds

The SDM SMG9 provided excellent results from the standing position, returning tight patterns with both Fiocchi “Top Target Plus” and GECO 9x21mm caliber, 124-grains loads: all shots ended up very central, even when dumping two magazines in rapid fire and using the hotter Fiocchi “Black Mamba” loads. 

We were assisted in our tests by a skilled shooter, and the accessories we had available helped him to achieve an even better control on the gun.

Was it just sheer luck? That may very well be; we will soon try the SDM SMG9 again in different conditions and with different loads (both factory ammo and handloaded) to see if its performance remains consistent. Sure enough, should that be the case, we would genuinely be surprised: the SDM SMG9 would be a true gem in the mud, well able to stand against several well-known counterparts on the market.

Sure, the SDM SMG9 also owes much of its stability to the overall well-distributed weight (2,5kg/5.51lbs empty, about 2,7kg/5.95lbs with a full 15-rounds magazine in) and to the rigidity and stability of its stock. The recoil level is extraordinarily low, even when dumping mags in rapid fire.

Conclusion

The SDM SMG9 is sold in a cardboard box including the gun, a single magazine, and no instruction manual whatsoever – probably the manufacturing company or the distributor should rethink the packaging. The magazines come out of the factory in a 30-rounds configuration only, but the Prima Armi company can limit them to 5, 10 or 15 rounds to meet local restrictions in several European Countries or elsewhere.
Practically speaking, the SDM SMG9 would be an exceptional small-sized carbine for range shooting, plinking or competition; it would also be a viable alternative for personal, home and property defense, and private security personnel or even Police in those jurisdictions where full-automatic weapons are only available to tactical units.
Its most direct competitors on the market are the MP5 knock-offs, the TP9 and APC models from the Swiss-based B&T company, and the extraordinary CZ Scorpion EVO-3 A1. The SDM SMG9 may be more spartan and austere in its construction, but when mass distribution will kick off, the retail price will also be much lower than what the above-mentioned, well-known competitors are sold for today. And that's not something to be taken lightly nowadays.