It's a terrible rule.
I realize the league doesn't want coaches tossing the flag just to delay the game and give the booth more time, but you can still penalize the team and review the play. Give them a 15 yard delay of game/unsportsmanlike, and take away the challenge. That would be fine, as long as you get the call right.
Another stupid, overly complicated NFL rule, the likes of which are killing the enjoyment of this league.
Automatic replays on TO's & scoring plays have to go. It hasn't worked out, it kills the flow of the game.