I've got the perk version running on a TF2 server I manage and it's always a big hit with the players. Unfortunately, when ZF is disabled, players are unable to get any crits. (Random ones, backstabs etc. still work) Also, the built-in disabler for ZF on non-ZF maps doesn't seem to function so I had to write my own.
Yea I have the sm_zf_force_on set to 0 and stuff like 2fort and what not still spawn with ZF running. Other than that the mod is great!