Thing i like about them is 4+ tough and medium bases and
SPD 6!
They are amazing at just getting in the way and 50% chance to not die is just gold. If any of them survive They can get up for free and just charge
Cygnar is probably the best to use boomhowler with as you get several spells which can be cast on mercenaries

like SNIPE! but why would you be shooting with boomhowlers
lol.
pCaine can give them deadeye and snipe! but then thats better off on stormblades... Blur to help them from being shot.
eCaine Heightened Reflexes might be awesome. Make them immune to knockdown with 4+ tough

thats just sneaky
Any caster with Arcane shield works on them.
eHaley with Deacceleration, affects FRIENDLY models ;D
Nemo's polarity shield So they cant be charge!
They will work well with anyone other then like darius and kraye who are Battlegroup specific, and brisbane has nothing to give but his feat.