I don't have any complaints about the Z2, it performs remarkably well especially for its price point.
Obviously doesn't have the same adjustability of the Fox Grip2 or Fit4 dampers for fine tuning, but I find its base tune pretty good anyway (3 vol spacers in mine). Supportive without being harsh.
I don't know if the Rhythm damper would really be much if any improvement, but I haven't owned a Rhythm to really compare just had the odd ride on mates.