We had that very discussion last night after a couple of these. Unless they're made by someone who knows what they're doing, bar and restaurant Margaritas are typically a major disappointment.
Hi, Simon - I evolved something very similar from the original Tommy's but use a 50:50 blend of agave and triple-sec (11ml each in the recipe above). I also use Bob's Margarita bitters, prefer the salt rim and serve it up. Had one last night. Quite excellent.