apeks and zeagle are identicle internally. both are excellent regs. if you live in the states i would not buy beauchat because of a low number of quality repair sites. don't get anything added to your apeks they are fine the way they are. in fact i am not aware of any performance enhancers out there for them. it would be a wast of money. the s600 is one of the top scubapro seconds but i would buy the g500 because the only difference is that it is not adjustable. and it is more reliable.