The H&K MP5SD6 is the first premium SMG available for purchase for new players. In previous renditions of the game, at least on the Kongregate version of the game, the H&K MP4SD6 was temporarily provided to new players for free upon creating a new account, with the rental period expiring after five days. As of August 2019, this is no longer the case, and instead, players are permanently provided with a free IZH-43 with unbroken status.
The H&K MP5SD6 combines some of the best performance aspects of the Kedr and H&K MP5K, the two credits-purchasable SMGs available in Set 1. This includes high accuracy, low recoil, a fast fire-rate, very high mobility, a very fast reload speed, a comfortable clip size of 30 rounds, and a high amount of reserve ammunition. However, like these other two SMGs, the H&K MP5SD6 has low damage, low penetration, high damage fall-off, and a low effective distance.
The H&K MP5SD6 is automatically equipped with a built-in silencer and built-in scope upon purchase. The built-in silencer allows the H&K MP5SD6 to be silenced without receiving any of the negative effects of regular silencers, such as less damage, penetration, and effective distance. Meanwhile, the built-in scope is actually a very good scope, with high zoom and a clear view. Other higher-tier SMGs can also unlock this scope through Weapon Customization, though at very high costs (experience, GP, etc). This scope appears slightly different on other SMGs; it is said that the H&K MP5SD6 possesses the clearest version of this scope.
Overall, the H&K MP5SD6 is a great weapon. It is actually decent in higher-level servers, though it is seldom used because most players dislike the built-in scope and prefer SMGs with higher damage (at the cost of lower mobility and occasionally a slower reload speed). The H&K MP5SD6 can be considered a near straight upgrade to both the Kedr and the H&K MP5K, apart from the fact that it lacks Weapon Customization.
While the built-in scope is quite good for the niche purpose which it serves, the player will probably find themselves being hindered by the scope most of the time, due to the fact that SMGs generally benefit more from collimators rather than from scopes. It is recommended that the player only use the scope for long-range combat, and instead fire from the hip in close to mid-range combat. In order to maintain accuracy, it is recommended that the player fire whilst walking (default button is "Shift"). The Sniper Skill "Dynamic Shooting", which can be unlocked quite early, will improve the accuracy of the weapon whilst walking.
The overall statistics of the H&K MP5SD6 make it a very good weapon for fast-paced close-range combat in small Deathmatch maps and in some medium-sized map like Evac and Terminal. However, like most SMGs, it will struggle to keep up against assault rifles, battle rifles, sniper rifles, and light machineguns in large maps like Old Sawmill, although with practice veteran players can take advantage of its good scope, high mobility, and high accuracy for LongShots.