Well I will start off by stating that I believe point for point Kans are one of the best units in the game. Dreads...i really dont like these. They are more points then 2 kans and do the same and are easier to kill then 2 kans. Never take Dreads... end of Tactica: Dreads.
Now back to my favorite unit: Killer Kans
For the cost of a termi you get a AV 11 walker and can get up to 3 in a squad. These are far harder to kill then termies for most things. They attack at initiative 2. That is kind of low but most things that will harm them are at I1. Grenades are just bad against them. S6 grenades will hardly ever kill a kan unless your opponent is rolling hot. S4 does nothing to them as well. Even their WS of 2 is not a problem because the average WS is 4 or lower.
Now to my tactics. These guys are the 3rd and crucial part to my 3 prong strategy. First are the fast things in trukks and my stormboyz arriving turn 2. Next my boyz mobs turn 3 and finally my Kans on turn 4 or 3 if they are lucky.
These guys run cover for my mobs and break off turn 3 in their movement and running so that the boyz can charge right through their hole. They just make sure more boyz get to combat. The next turn they will follow up any blown combats and typically wreck anyone left. They also are great for chasing vehicles and making sure my boyz get the charge. With their forward placement you have to move around them to get at the squishy goodness behind the kans. In addition to everything they take a lot of fire turns one and two because they are closer then the boyz. This distracts the hard hitting weps from going after my nobz or stormboyz. Another important thing to look for or ask is where are the powerfists. Why? Most squads without them just sit there doing nothing to the Kans while the Kans just wreck the squad. Also IG blob squads will just stand there watching these guys kill and kill while the sargents throw grenades and pray for a 6.
Well that may have been a very short discombobulated Tactica but I hope you get that they are very good at a lot of things and to consider running them in your lists.