They honestly give one of my regular opponents fits. They are about as tough as grots, not really, 1 less wound of course, but their melee threat is about the same and their shooting is amazingly good. 6 in the tantalus with 2 medusae and Archon regularly delete things. Their demon prince death count is depressing if you're chaos. 18-30 shots depending on how many you use, rerolling with splinter racks will put out a ton of wounds while tough 5, 2 wounds and fnp (hopefully with cover) makes for quite a resilient/killy HQ bunker.
For Khaela Mensha Khaine!