I couldn't resist grabbing some of these when they were revealed by Forge World earlier in the year:
The Thallaxi Cohort has access to some nasty weapon options in addition to their already formidable armaments. After a fantastic brainstorm chat with Ead Brown at Forge World I decided to go with the phased plasma fusil to give me the ability to tear up more power armoured Traitor Astartes. As there's no 'official' version of the weapon yet I converted one of the Thallaxi's lightning guns (left most model in the above image).
And here's the Cohort part way through being painted up:
I decided to paint their face plates glossy black as I wanted them to appear as inhuman as possible. I've also deliberately restricted the colour palette so that it's easy to replicate and because I don't see the Mechanicum as adding embellishment where it's not necessary. In the picture below you can see the glowing cores of the atomantic arc reactors that power the Lorica Thallax as well as the various thrust nozzles that make these heavy infantry scarily manoeuvrable:
This is but the first unit of a Crusade/Heresy Era Mechanicum Army that I plan to build up slowly as more units are released by Forge World.