Codex: Skitarii is not even out yet, but just looking at the confirmed rumors (i.e. ones where we actually have pictures of data sheets with no-kidding rules), we have the following on the Sydonian Dragoons:
Looking through the unit profile, this light walker can be taken in units of 1-6, has 4 x S8 AP- I6 per walker on the charge (so 24 attacks from a full squadron of 6 Dragoons).
-Close Combat –Taser Lance grants an additional +2 hits for every roll of 6+ to Hit (kind of like Necron Tesla weapons). This means that, on average against a WS4 opponent, a 6 walker squadron of Dragoons would have 24 attacks, 12 hits, 4 of which would be 6+s and so generate another 8 hits, for a total of 20 hits on the charge. At S8 and I6, these would wound pretty much anything but Wraithlords/Wraithknights on a 2+ and strike before all but the best close combat units in the game. Of course, the target would get armor saves, but with 20 hits and probably between 16-17 wounds, most targets are going to fail enough saves to take some serious damage. Better yet, at S8, this is causing ID to anything T4 or below, so only a single wound has to get through to take out multi-wound models.
Against vehicles, this gets even better. 24 attacks, hitting on 3+s, means an average of 24 hits (after extra Taser Hits are added in)…. S8 vs the AV10 of most vehicles rear armor (that includes you, Wave Serpents!!) means you are glancing on a 2+, so about 20 glances on the charge. Even if you multi-charge (and so get less attacks, due to Disordered Charge), that should still be enough to kill multiple vehicles at once (again, what a great counter to Wave Serpent spam!). Even AV14 Land Raiders can be glanced to death, with on average 24 attacks, 24 hits, and 4 glancing hits after the smoke settles (so 4 HPs gone, one Land Raider dead). As you can see, a squadron of 6 Dragoons is quite versatile and potent in its damage output against the spectrum of targets (and an entire squadron of 6 Dragoons only costs just under 300 points, so VERY affordable).
-Mobility — Sydonian Dragoons have the mobility that really all walkers in the game should have (I mean, should a giant Dreadnought be able to move quicker than an infantryman 1/4 its size?). With the Dune Strider special rule, they can move 9″ every turn, then either run D6+3″ or charge 2D6 +3″… combine this with Crusader (which not only helps in winning Sweeping Advances, but allows improved Run rolls), and you should easily be able to move an entire squadron between 15-18″ across the board Turn 1, setting them up for a very reliable Turn 2 charge (which itself has a better threat range, due to the +3″ added on the charge range). Overall, this mobility makes them very good at their job and strong value for their points (it also helps them seize objectives as well).
-Survivability — While only having AV11/11/11 and 2HPs each, the Dragoon’s Incense Cloud rule gives them a permanent 5++ cover save against shooting. This is decent, but still means they are pretty fragile, until you add in another factor… allied Psykers casting Shrouding (from the Telepathy discipline)… this area of effect Blessing means you can buff multiple Dragoon squadrons around the Psyker at once with Shrouding USR, brining their cover save up from a 5++ to a 3++… now, all of a sudden, they are MUCH more survivable and can reliably soak up a lot of fire power while using their high mobility to cross the battlefield, then get off that critical charge on turn 2+. Of course, this is dependent on getting the Shrouding power and then having enough Warp Charges to get it off reliably, but done properly it can make multiple squadrons of Sydonian Dragoons truly a force to be feared.