There was a thread on “sodium citrate failure.” The OP’s problem was that things didn’t work out as promised and she ended up with a separated failure.
In my case, it worked beautifully. I obtained the promised smooth emulsified cheese sauce. Problem: the consistency was simply not pleasant to me. It looked creamy, but when you ate it, that is, stuck a fork into whatever you were eating (in my case, shells and cheese), it was stringy. Not oily, stringy.
I hated that. Plus, I like the slightly diluted taste of flour and butter and milk that make up the white sauce. To a purist that is supposed to be a fault because it taints the pure taste of the cheese. I like it.
Just a personal taste. Sometimes the fussy old way is better.