With a small but very fit squad it seems sensible to use all means available to detect when a playing is fatigued to the point that the next step might be injury unless replaced. Might be only a couple of minutes before the player would have been replaced anyway but things can go undetected visually on a field when so much is going on during a game so I can’t see a problem with it TBH, it’s an aid to assist decision making that’s all.
