Is it safe to use e85 fuel on a 2014 ford flex

If it says "flex fuel" in the name then yes you can use E85 in it.

You will get poorer fuel economy with E85.

E-85 will increase performance slightly due to it's higher octane rating. E-85 has less energy than regular unleaded gasoline so there will be a drop in MPG. E-85 is cheaper than regular gasoline and burns cleaner and it makes less pollution. It will still cost about the same per mile so there are some benefits and some downsides. It is a 6 of 1 and half a dozen of the other proposition using E-85 versus Regular Unleaded which is E-10 in most parts of the USA.