This is in response to this thread on DIR Explorers. As can be seen there is NO functional difference between the different models of apeks 2. stage regulators.
The only differences are that the shuttle valve on the T20 is 49.18mm vs 48.90 on the XTX40 and that the counter balance cylinder on the T20 is 22.57mm vs 20.25 on the XTX40
Please note that the main difference between the 20 series and the 40,50,100 and 200 2. stages is the heat exchanger is replaced with a plastic spacer on the 20 - as can be seen on the picture.
After less than a year of use the handwheels on my DS4 1. stages started to fall apart, forturnately Apeks was very helpful in resolving the problem. My DS4 1. stages are now fitted with nice and shiny all-metal handwheels