Both the 340 and the 350 have the same first stage (R-300) which has a balanced diaphragm, two H.P. ports and four L.P. ports; there is DIN version available. The 340 is the base model with an adjustment breathing knob. The 350 has two second stage filters, the 1st is an active carbon filter which cleans the breathing gas, and the 2nd is a metal fiber filter that catches small particles - according to TUSA, these filters eliminate the need for an adjustment breathing knob.
The 460 uses the R-400 first stage which has a balanced diaphragm and is environmentally sealed. It's rated for cold water and the first stage can be converted from a yoke connection to a 300 bar DIN connection.