A brindle is always very easy to spot - with that long spikey dorsal fin and pig face, it looks just like a prehistoric dinosaur to me. And that's generally the first thing I see when I see one in the water - that dragon back. Also the fish normally looks pretty black in the water - esp. in poorer viz.
The malabar has a classic rockcod look about it, while the brindle doesn't. If you see a big cod-like fish and it doesn't have a spikey dragon back, then it's almost certainly not a brindle. The other large black cod that you might mistake for a brindle is a purple rockcod, but again the purple looks like a rockcod - it's very easy to see. Other big cods like the malabar, orange spotted, etc all have the large head, large rockcod lips and good looking colouration. The brindle has a small piggy head (the head can look too small for its body) and the tell-tale spikey back.
Very easy to spot!