I see it when playing back demos, but not in games. Is there a minimum server version or server cvar to let clients use it in regular games?

It's not a gameplay feature; It's for spectating only, like radar and hud_teaminfo on both teams.

It only works for mvds or mvd streams (ie. qtv) because it requires constant data on all items which doesn't get supplied to in-game players or spectators.

Ahh, figured as much, thanks.