I share exactly the same experience like Panini. When I first got to BsAs last year I also thought that La Cabrera is great, I went there a few times, but after living here a while I realised that there are way better options (quality/price) than La Cabrera.
However, I went there last week with some friends that are visiting (that are not used to Argentine cena hours yet) so I thought with the 40% discount it's not bad option. The atmosphere was stressed and the waiters not attentive at all, the service was miserable (we got the steaks at 7.45h, so theoretically had 15min to eat plus we got the side dishes 15min before the meat so all of them were cold by the time the meat arrived, the waiters didn't respond to this) and yes, everything ridiculously overpriced, so with the 40% your bill comes to the same as in a more authentic parrilla with better atmosphere