Pay attention to job specifications, if there are any. In many specs, especially public works, steel flex is specified, and therefore aluminum flex would not comply. Remember, engineers do not have to install the stuff.
One other issue, there are cities in and around the Los Angeles area where approved types of aluminum flex conduit can be utilized as the grounding path, even when the length exceeds 6'. I believe it's 100' for 1/2" Al-Flex, less for 3/4", and less again for 1".
There are problems with the interpretation of this ruling, and it does not apply in all cities. Without saying this is a good or bad idea, many local contractors take advantage of the savings by not providing ground wires when installing Al-Flex.
Radar
