We visit this restaurant every time we are in Mexico City (one or twice a year). They have exceptional service (particularly compared to American standards). They hot chocolate and bread are tasty but if you want a fun little show order a lechero. The lechero is a coffee with milk, they pour coffee in a cup and then top it off with milk by pouring with the steaming milk pot held at arms length over their head.
I recommend the huveos divorciados or egg white omelette (filled with cottage cheese).
We tip very generously and when we are in the area we use the restroom here, even when we are not having a meal, because they are so clean. If you tip well and are polite to the waiters they will remember you and wont have a problem with you stopping by to use the facility.