I have a dm4 and a borg. I switch around between the two markers but I always seem to come back to the DM4 when I am playing a tourney or some key game. I just seem to be able to hit things with it
I tried to figure it out recently and I think its the fact that the spool valve has a very balanced movement when it fires and this really seems to allow me to hold onto a target better and place ball on ball far easier. While I think the borg is really solid, I still notice a different action of the marker that makes me come off the target and reposition slightly between each shot.
This is JMHO and you should try both, either marker a is pretty good choice.