IIRC the fluidampr is a really heavy unit and some seem to think that this could cause the engine to not spin up as fast and could also cause damage to the crank in high RPM motors. I would go with the SOcal on also.
alot of the cummins guys use fluidampr and we had no problems yet. the only problem with it is you have to have a billet cover to run on a cummins. but we are running over 5000 rpm on mine with the fluidampr.
I ran one for 2300 miles and now my cranks broke, I guess the floor is open but I'm switching to the ATI Super Damper, To my knowledge it's about $50 higher but weighs a pound less than stock, my crank broke up front.