Shunt needed when I have Orion xs?

hi,
I have a simple question … I have a van with 2 batteries (starter, board) and intend to setup a Orion xs as DC DC booster … and also have a shunt I wanted to hook up on the starter battery but I realized that in Orion xs app I see both starter and board battery voltage
is there any benefit in still adding the shunt ?
Thanx in advance