High performance regulator kit!!!
This is a combination of the US4 1st stage (exactly the same as the DS4 but without a cold water kit) and the AT20.
The particularity of the Apeks regulators is precisely to make all their 2nd stages have the same performance, differing from each other in having or not cold water kits, adjustment by dial of the respiratory effort (only in the XTX50, 100 and 200) and aesthetics .
This is therefore a very good option as a high-performance regulation in case it does not have to be exposed to cold waters