I'm growing a number of copy cat greens this fall. These two greens definitely fall into this category. I wouldn't be able to tell them apart unless they were labeled.
Tokyo bekana (on the left of the top picture) might have slightly bigger leaves. Since everything is grown densely in containers I can't really say this for sure.
Fun jen leaves might be slightly more ruffled. Again, I can't really say for sure. Either way, they are both really good, fast growing, crunchy, mild flavored greens. I would grow either in my theoretic garden, but probably not both.