I now have two 600s. Being left-handed but almost ambidextrous I have two sets of grips for both. Nothing is more fun than holding one in my left hand, the other in my right and just shredding a target with rapid firing from both.
Both have the turn back piercing caps - no problem at all and I think that they look better.
I bought the first in February and have got through 16000 pellets since- thats over 500 CO2 cartridges. Best fun ever.