With 7 hull points and 13 armour on the front, they have a very reasonable stat line (although the 12 armour on the other facings will make the player think harder about positioning and angle). They are able to be configured in every manner (Paladin, Errant, and so forth). Hence the flexibility that this knight offers is good and when combined with the relatively quick movement of 10, they really do pose a good threat to most things on the table.
Weaknesses.
Massed firepower can and will bring down knights with this chassis - make no mistake. Although it won't explode, the controlling player really does need to think carefully about optimizing the build and purpose of these beasts.
Builds.
There are many builds available here. I'll go through some of the more common ones.
Knight Paladin, Reaper Chainsword, Batle Cannon, Stormspear Rocket Pod (405 points).
A classic set up which is mid range and a bit of a swiss army knife able to take on many roles. I added the storm spear because why not.
Knight Errant, Reaper Chainsword, Thermal Cannon (380 points).
Up close and personal. Tanks and heavy infantry are your targets here. Take the front mounted melta gun for added fun.
Knight Crusader, Battle Cannon, Gatling Cannon, Twin-Linked Icarus Autocannon (415 points).
Long range fire support, and anti-air to boot.
Knight Gallant, Reaper Chainsword, Thunderstrike Gauntlet, Ironstorm Missile Pod (410 points).
Melee knight.
Knight Warden, Thunderstrike Gauntlet, Gatling Cannon, Ironstorm Missile Pod (415 points).
A mixed bag. Good against lighter vehicles and infantry.