Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

Possibly a stupid question, but what's the hard bit? Because of low internal flange making it a bitch to thread the spokes or something else?

They don't take sapim cx ray either, do they?

You end up with horrible balance of DS/NDS spoke tension.