I don't know whether opposing units like tanks or TD's target the crew or the weapon. I do know it's not easy to use and easy to wipe. The nominal range is 120, but it is so bad at that range that you aren't going to wipe anything. It takes forever to fire so it gives the other side plenty of time to attack it. The PWerfer and Calliope also have to get close but at least they fire quickly and can retreat quickly.
If I was going to rank it, I'd rank it last among the rocket arty.
If you got the number from cruzz's spread sheet that is the size when it does not have a crew.
It probably uses a different size when it has a crew.