Since you are asking about AE, then we can say that "off of" means the same thing as "off." The woman got off of the MRT. = The woman got off the MRT. The boy took his feet off of the seat in front of him. = The boy took his feet off the seat in front of him. Most Americans use "off of" all the time, at least when speaking. So, it is standard in everyday American speech (and in some writing). I would not recommend that you use it in formal contexts, such as in formal writing or on a test or business communication. But feel free to use it in speaking English with your friends, if you are not afraid to sound like an American. Sources for my answer include: http://www.thefreedictionary.com/off http://www.merriam-webster.com/dictionary/off%20of http://english.stackexchange.com/questions/101683/difference-between-get-off-of-and-off

Canny Brits do use 'off of' when it suits them, though : when it comes to getting a lyric to scan, and making a fortune: 'Hey, you. Get off of my cloud!'

The difference between them, is that "off of" is used by Americans. For English and other British people, saying "off", would be sufficient. Saying "off of", is not really necessary. It is an example of, American English involving words that are superfluous. Unnecessary, added extras.

also, be careful. In america, by itself, the term "get off" can be used in sexual contexts. (ie: to have a thrill, gain sexual excitement/satisfaction ) " he gets off at watching porn " "he gets off at seeing his girlfriend in high heels" " that gets him off " " she/he gets off on it"