They're 2 different pistols,
The Rohm is a 5 shot suitable for informal target, rapid fire etc the 6004 is purely a 6yrd/10mtr paper puncher,
The Rohm is a good pistol for the money however there is an issue now with parts, seals are Ok but anything more can be a problem as no longer available from the manufacture and availability of remaining stock ran out a while ago, Magicniner does now make some parts for these.
The 6004 would likely have a better trigger however there have been quality issues, They are a far cry from the original FAS604 which was superb and can be bought 2nd had for around £200-£250, a far better buy imo, (and will hold it's value)
The Rohm will have better power if you are looking to shoot at a distance past 10mtr.
The B96 is as good as either if set up correctly,
hope that helps.