The Ref 150 is the only one in the series that does not have meters. Both the Ref 75 and Ref 250s have the meters. I think it is because they wanted to use the same casework as the Ref 110.
It all depends on your speakers. My speaker are relatively efficient at 93db. I still preferred the Ref 150. I liked the extra headroom and I thought the bass was just a bit crisper.