I'm not sure if this is the current model for this guy as I stopped playing near the beginning of N3. But basically if there was a big smooth looking robot on the field for the combined army it was one of these guys.
Which meant a couple of things.
1 they could not be in loss of LT unless there were only irregular orders left in the army or you EM everyone.
2 the sepsitor, and monofilament weapons were both on the field. So they may try and rush with the EI fragment to try and steal your troops, or bait you into melee.
3 it has some kind of horrible gun. The least destructive these things got was a plasma rifle which they were quite good with.
4 no sectorial army. These guys were great, but weren't available in sectorial armies.