Absolutely love these bugs! And they’re the new hotness since the BOB and chapter approved books.
I have two and I normally end up running both (Unless I’m going full kraken). I’ve been giving both the 5++ count as double wounds for degradation chart adaptation. They’re biggest flaw is they’re durability. They need babysitting with a malanthrope for synapse and the -1 to hit.
I used to run them Jormangandr for the 2+ save (fantastic counter against Deathwatch who wound these guys on 2’s with storm bolters) but since the new Kronos spell, they’re a mainstay in a Kronos detachment now. The in built +1 to hit makes the spell trigger additional shots on 5’s which really helps pick up the misses.
They’re new strategem is sweet too, because LOS
is a problem. So moving and still counting as stationary can really come in clutch.
The adaptation to cause mortal wounds with them is a trap IMO. They become target priority number one. They can do plenty of damage with the Kronos pell and pathogenic slime strat.
My advice if your running them, give your opponent a more pressing first turn threat. My favourite is the genestealer sling shot. Absolutely has to dealt with or suffer severe losses and leaves Exo to do work.