I might be wrong, but I think the Electric Mistress came out before the first Chorus pedal, which might be the boss one. The Electric mistress is also a different 'flavour' from most flangers, it's not really designed with the fighter jet sound, it's got a very musical and watery tone. The other really big user of the pedal was David Gilmour, if you hear any modulation effects from Animals up until The Final Cut, it's the EHX EM flanger.
I have no doubt that the clone theory can do that, choruses and flangers are based off of the same design ideals, and are (on milder settings) just two different ways of achieving the same thing. Both function as a tiny delay, I'm talking fractions of a second, so small a delay that it sounds like both notes are going off at the same time, though there are some more expensive chorus pedals with a 'time' option where you can drag it out a bit.
This is where they differ, on the second signal, the 'echo', an effect is added. On the Flanger, this is a filter which sweeps through the frequency range. On a chorus this is more likely a light vibrato effect to pull the tunings of the notes, though cheap choruses sometimes don't add a secondary effect. Frequency VS Pitch, essentially. This time-delayed and effected echo is blended with the original signal creating the effect. Like I said before, they are two variations on the same theme. Phasers also work with a time-delay but I actually don't know how they work on the inside other than its a time-delay with a 'phase shift'.
Sorry if you feel I'm being condescending with this, I just find the stuff super fascinating so I wanted to type a few paragraphs about it!
