If that is the plastic side extensions with the pins ( not sure as I have the df 700 ) then I say yes they are useful.
I have used them quite often on longer tabletop glue ups etc. It means you can index without measuring over a longer distance.
I do find you have to keep checking they are locked into the body firmly as they are not super secure, at least on mine they try and work loose.
The other adaptor for centering the end of legs or smaller components is handy on occasion as well.
