Had 2 dozen games or so with them since 8th came out.
Onagers hanging out in the back with Cawl put out some good damage. Neutron Laser will eat anything alive and Icarus Array will hit a surprising number of things on 2's since so many things have the 'fly' rule now. The hitting non-fly on 4's after modifier isn't that bad since Cawl can reroll any hit rolls.
The destroyers definitely can delete some stuff if you kit them out Plasma since it's D6 shots and if you stick and Dominus by them you can overcharge relatively safely.
Vanguard do surprisingly well against vehicles and monstrous creature stat lines. With a squad of 10 without special weapons you can put out 30 shots, reroll 1's with a Dominus, and even though you are wounding on 6's that 6 also does a mortal wound; maths averages 5 mortal wounds from a full squad, including rerolls. Tournament last weekend I had a squad of them bubble wrapping Cawl and my Onagers and they did 6 mortal wounds in one round to a very sad Terminator squad trying to get in.
I stopped using Rangers with Arquebuses. The sniping characters is cool but they really don't put out enough shots to do any real damage, even with the chance of mortal wounds.
I will say I have used another detachment with a cheap inquisitor and 3 distraction assassins. A Calidus and 2 Eversors will pull the heat off your mechs and can reliably take out the backfield Conscript/Cultist objective campers. My current list I added a cheapo Knight to be a big target and some conscripts to better camp objectives.
With the AdMech Codex coming out after DeathGuard hopefully they will adjust some numbers some or give us a transport at the least.