If you have Co2 for your marker , then this is important.
Some markers cannot work with liquid Co2. This device sits in the bottle , and should extract the vapour that sits above the liquid. Hence ( Anti-Syphon ) , however , if you hold the bottle upside down , the end of this tube goes into the liquid , and becomes a syphon tube. So be careful.
Some markers work better with liquid Co2 ( VW68 , PMI3 etc ) , and some will stop working and will need this ( Automag etc )