This seems very strange for a master tactic (worth noting it wasn't in the playtest at all, so probably had less time to be edited).
There's no mention of the action cost for the primary squadmate, but it's a reaction for any squadmate who helps them. And unlike every other master tactic, it has no cooldown.

I'm inclined to rule it costs no action for the primary squadmate absent any other indication, but it feels a little strange to have the tactic be a 1-action no-cooldown MAPless Trip in that case.