Tzac doesn't exist in final version yet, there is no client for linux, neither for mac and it is bugged on windows, some people cannot even install it on windows because of data loading bug.

I use it anyway because i want to play in the ESL ladder but this is not an alternative to punkbuster while i need to start windows exclusively for it.

Punkbuster still exists because we can create etkeys or use old one but it will be outdated in the future anyway. It is needed to finish the development of tzac for all mods and platforms.