The bottle-service component is unique to the South Beach location because, well, it's South Beach. You can fork over $150 for a bottle of Absolut, which comes with mixers as well as a tray of accroutrements (crisp mortadella, fontina cheese, celery, house pickles, and olives), or you can get bottomless bloody marys (made with Absolut) for $35 per person. Granted, the accoutrements cost an additional $20 if you go bottomless, but if you compare how many drinks you'd get from a bottle for a group of, say, five (where everyone would pay $30) to as many as you want, it's a no-brainer. Perhaps bottle service should be left to the clubs, even if this is a party brunch.
As for the food, Siena has brought over all the Chi-town staples and added a few Miami-centric dishes.
A popular item on the regular menu, coccoli, has been given an inimitable brunch twist. For dinner, the crisp dough balls are served alongside stracchino cheese, prosciutto di parma, and truffle honey. But at brunch, these fritters are paired with salmon and lox ($18). "Our chef was like, 'Wait a minute -- I'm Jewish. Why don't we have this?'" Pro tip: Cut your balls in half to create a pocket for your smoked salmon, cream cheese, capers, and onions.