Hi,
The Nagaoka should be better on a 16.5g arm. Grados like arms of a little lower mass.
Oddly enough the 2M is slightly higher compliance than the Grado, but the Grado suspension is undamped and they're touchy about appropriate arms. They also interact badly with certain platters. I think there's a compatibility chart somewhere on Karma.
The stylus can be upgraded on the Ortofon. The Blue should be smoother and somewhat more resolving. The bodies are identical. The Bronze and Black are slightly different, but the styli will fit. Don't know if the 2M is part of the deal or not. If so, maybe this is pertinent.
neo