1. You can use bar feeder as support for small bar till machine is capable to pull it with tool in the turret.
2. You can use bar feeder as simple bar puller and machine will take required length.
1 and 2 applications don't require much from the bar feeder.
So, it is worth anyway. If bar feeder appears to be capable to work properly with many functions, then You need the machine interface. If Your lathe has bar feeder interface built in?